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Cited by 1Values and Moral EducationPsychological Well-being and Life SatisfactionBullying, Victimization, and Aggression

Girls are made of sugar and spice and everything nice, but what are boys made of? A randomized control trial suggests the effects of a school-based kindness intervention vary by gender

Open access
Hinton, Christina, de la Rosa Fernández-Pacheco, Pedro Antonio, Caro Samada, Carmen, Okuzono, Sakurako S., Hill, Ben, de Gregorio Vicente, Oscar, Moller, Francisco·2025·Journal of Moral Education
DOI 10.1080/03057240.2025.2509821
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Abstract

While previous research suggests that kindness interventions in schools can effectively increase kind behaviors, more randomized controlled trials (RCTs) are needed, particularly those examining gender differences. To address this gap, we conducted a matched-pair cluster-RCT with students aged 10–13 in the UK and Spain, analyzing results by gender. The intervention, lasting eight weeks, combined an acts-of-kindness scavenger hunt with weekly journal reflections. Results showed an increase in kindness among girls, but not among boys. Unexpectedly, boys showed increased anxiety following the intervention. This gender difference may stem from the type of kindness promoted—more relational and reflective—which girls may find easier to adopt. It may also relate to girls having more psychological resources for such activities. These findings highlight the need to consider gender-specific responses when designing kindness interventions. They also raise broader questions about how to differentiate character education to ensure it is effective for diverse learners. Addressing these nuances can improve the design and impact of programs aimed at fostering prosocial behavior in young people.

Integrity signals

Registry

Crossref · 10.1080/03057240.2025.2509821

Cites

56 of 56 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

1 of 44 cited sources checked · 1 supported · 0 flagged · accuracy not yet measured

  • Premisecitation

    Boys tend to conceptualize kindness through themes of helping physically and in heroic or chivalrous ways.

    “Research suggests that boys, in contrast to girls, tend to conceptualize their kindness through themes pertaining to helping physically (J.T. Binfet & Gaertner, 2015) and in more heroic or chivalrous ways (Eagly & Crowley, 1986;Maccoby & Jacklin, 1978)”
    Quote in the paperSubstantial claim1 of 3 sources checked
    • cites J.T. Binfet & Gaertner, 2015

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites Eagly & Crowley, 1986 source
      Experimental — accuracy not yet measured
    • cites Maccoby & Jacklin, 1978

      Not checked in the free run.

  • Findingown data

    Boys in the intervention group showed a significantly greater increase in anxiety symptoms compared to control (beta = 0.28, 95% CI = 0.07, 0.48, p = 0.010).

    “Boys in the intervention group showed a significantly greater increase in anxiety symptoms compared to those in the control group (beta = 0.28, 95% CI = 0.07, 0.48, p = 0.010)”
    • Also stated in: § Discussion · plain
      “unexpectedly, found a significant increase in anxiety among boys”
    Quote in the paperSubstantial claim
  • Findingown data

    No strong association was observed for anxiety among girls (beta = 0.11, 95% CI = -0.11, 0.33, p = 0.312).

    “while no strong association was observed for girls (beta = 0.11, 95%CI = -0.11,0.33, p = 0.312).”
    Quote in the paperSubstantial claim
  • Findingown data

    The effect sizes were modest in both cases.

    “The effect sizes were modest in both cases.”
    Quote in the paperNot a substantial claim
  • Findingown data

    The increase in kindness among girls was not observed among boys (beta = 0.04, 95% CI = -0.14, 0.21, p = 0.677).

    “This finding was not observed among boys (beta = 0.04, 95% CI = -0.14, 0.21, p = 0.677).”
    • Also stated in: § Discussion · plain
      “we did not find an increase in kindness in boys”
    Quote in the paperSubstantial claim
  • Classified as probably not a substantial claim. 36
  • May combine two claims. 15
  • The quote only partly states this claim. 1

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Findingown data

    Results did not change significantly after excluding pairs from matching classrooms with different ages.

    “Similarly, results did not change significantly after excluding the pairs resulting from matching classrooms with different ages from the analysis.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Findingown data

    Results were very similar with complete-case analysis, with slight variations at the centesimal level.

    “Results were very similar with the complete-case analysis; there were slight variations in the estimates at the centesimal level (Table 4).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    Overall, kindness scores were higher in the intervention group, but the difference was not statistically significant (beta = 0.08, 95% CI = -0.04, 0.20, p = 0.206).

    “Overall, kindness scores were higher in the intervention group, but the difference was not statistically significant (beta = 0.08, 95%CI = -0.04,0.20, p = 0.206).”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim.

    Findingown data

    In the case-complete analysis, the kindness intervention had no statistically significant effect on anxiety symptoms among girls (beta=0.11, 95% CI -0.11 to 0.33, p=0.341).

    “Girls | 0.11 (-0.11, 0.33) | 0.341 | 1.44 (1.00)”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim.

    Findingown data

    In the case-complete analysis, the kindness intervention had no statistically significant effect on kindness in the whole sample (beta=0.07, 95% CI -0.05 to 0.19, p=0.240).

    “Whole sample | 0.07 (-0.05, 0.19) | 0.240 | 1.34 (1.00)”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim.

    Findingown data

    In the multiple-imputed analysis, the kindness intervention had no statistically significant effect on anxiety symptoms among girls (beta=0.11, 95% CI -0.11 to 0.33, p=0.312).

    “Girls | 0.11 (-0.11, 0.33) | 0.312 | 1.46 (1.00)”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim. The quote only partly states this claim.

    Findingown data

    In the multiple-imputed analysis, the kindness intervention had no statistically significant effect on kindness among boys (beta=0.04, 95% CI -0.14 to 0.21, p=0.677).

    “Boys | 0.04 (-0.14, 0.21) | 0.677 | 1.23 (1.00)”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim.

    Findingown data

    In the multiple-imputed analysis, the kindness intervention significantly increased anxiety symptoms in the whole sample (beta=0.21, 95% CI 0.06 to 0.36, p=0.006).

    “Whole sample | 0.21 (0.06, 0.36) | 0.006 | 1.72 (1.30)”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim.

    Findingown data

    In the multiple-imputed analysis, the kindness intervention had no statistically significant effect on kindness in the whole sample (beta=0.08, 95% CI -0.04 to 0.20, p=0.206).

    “Whole sample | 0.08 (-0.04, 0.20) | 0.206 | 1.35 (1.00)”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductown data

    The study protocol was preregistered in the Open Science Framework.

    “The study protocol is preregistered in the Open Science Framework at: https://osf.io/d5arn?view_only= 08a7e40c29524b6698ce789a5b7e7821”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Interpretationcitation

    Differences in effects based on gender might be partially explained by girls having more psychological resources to engage in the kindness activities, on average.

    “it is also possible that the differences in effects based on gender might be partially explained by girls having more psychological resources to engage in the kinds of kindness activities in the intervention, on average.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    The benefits of differentiated instruction for teaching academic subjects such as reading or math are well established.

    “The benefits of differentiated instruction for teaching academic subjects, such as reading or math, are well established (Aguhayon et al., 2023;Little et al., 2021;Magableh & Abdullah, 2021;Prast et al., 2015).”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites Aguhayon et al., 2023

      Not checked in the free run.

    • cites Little et al., 2021

      Not checked in the free run.

    • cites Magableh & Abdullah, 2021

      Not checked in the free run.

  • May combine two claims.

    Study design and conductown data

    Most assessed scales had intraclass correlation higher than the a priori assumed 0.05, with kindness around 0.2 and anxiety around 0.3.

    “most of the assessed scales had an intraclass correlation higher than the a priori assumed score of 0.05, with kindness and anxiety scoring around 0.2 and 0.3, respectively.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    Because boys and girls tend to understand and express kindness differently, and the intervention encouraged acts that resonate more with girls, it makes sense that the intervention was effective for girls but not boys.

    “Given that boys and girls tend to have different ways of understanding and expressing kindness, and the intervention encouraged acts of kindness that tend to resonate with girls more than boys, it makes sense that the intervention was found to be effective for girls but not boys.”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim. May combine two claims.

    Premisecitation

    Girls are often expected to be more nurturing and empathetic, while boys are often socialized to be more independent and less expressive of emotions.

    “while girls are often expected to be more nurturing and empathetic (Cole et al., 1994), boys are often socialized to be more independent and less expressive of their emotions (Leaper & Friedman, 2007).”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites Cole et al., 1994

      Not checked in the free run.

    • cites Leaper & Friedman, 2007

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S2 (checkable), S3 (load-bearing).

    Interpretationreasoning

    The intervention's items might have been within the zone of proximal development for girls and beyond it for boys.

    “might have, therefore, typically been within the 'zone of proximal development' (Vygotsky, 1978) for girls and thus offered an optimal opportunity for skill development that effectively stretched their capacity for kindness.For boys, by contrast, the items might have been more likely to be beyond their 'zone of proximal development.'”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites Vygotsky, 1978

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S1 (asserted), S3 (load-bearing).

    Interpretationreasoning

    If boys have fewer psychological resources and more difficulty expressing kindness in the intervention's specified ways, the reported increase in anxiety could be due to awkwardness and uncertainty in acquiring new complex skills.

    “If it is true that boys, on average, have fewer psychological resources to draw on in certain socialemotional domains and more difficulty expressing kindness in the ways specified by the Spread Kindness Like Confetti intervention, then it is possible that the reported increase in anxiety could be due to awkwardness and uncertainty in acquiring new complex skills.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim.

    Study design and conductcitation

    Kindness was measured with the School Kindness Scale.

    “These questionnaires included the School Kindness Scale (J.T. Binfet, 2015)”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites J.T. Binfet, 2015

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Study design and conductnone given

    Missing values were imputed using the Markov chain equations method, generating five imputed datasets.

    “missing values were imputed through the Markov chain equations method for multiple imputations.Five imputed datasets were generated for the analyses.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductcitation

    Anxiety symptoms were measured with a validated instrument.

    “including one that measures anxiety symptoms (Chorpita et al., 2000)”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites Chorpita et al., 2000

      Not checked in the free run.

  • Classified as probably not a substantial claim.

    Study design and conductown data

    After matching, classrooms were randomized to intervention and control groups.

    “After matching the pairs, we randomized the classrooms to the experimental group and control group.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductown data

    The quality of randomization was evaluated by comparing baseline characteristics between intervention and control groups across each country.

    “We evaluated the quality of randomization by comparing the baseline characteristics between the intervention and control groups across each country.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Study design and conductnone given

    In this study, randomization was conducted at the school level, and classrooms were matched based on proportion of boys and girls and age to minimize potential biases related to school composition.

    “in our study, randomization was conducted at the school level, and we matched classrooms based on the proportion of boys and girls and age to minimize potential biases related to school composition.”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim. May combine two claims.

    Premisecitation

    When educational activities are too challenging, students do not learn as effectively and may experience anxiety.

    “When educational activities are too challenging for students, students do not learn as effectively and may experience anxiety (Csikszentmihalyi, 1988;Vygotsky, 1978).”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites Csikszentmihalyi, 1988

      Not checked in the free run.

    • cites Vygotsky, 1978

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S2 (checkable). May combine two claims.

    Interpretationreasoning

    Boys might need more support in acquiring related psychological resources and/or more time to assimilate learning in this type of kindness intervention relative to girls.

    “This would suggest that boys might need more support in acquiring related psychological resources and/or more time to assimilate learning in this type of kindness intervention relative to girls.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Study design and conductown data

    Four sensitivity analyses were conducted: complete-case, full-respondent, excluding different-age pairs, and E-values.

    “Further, we conducted four sensitivity analyses.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Study design and conductown data

    The final sample had a completion rate above 95% for wave 1 in England and above 98% in Spain.

    “The final sample had a completion rate of above 95% for wave 1 in England (Wave 1 = 95.5%,Wave 2 = 97.7%)and above 98% for in Spain (Wave 1 = 98.6%;Wave 2 = 99.2%).”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Study design and conductown data

    Students were not informed of their assigned group or the aim of the intervention.

    “students were not informed of their assigned groups or the aim of the intervention.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationreasoning

    The lack of evidence supporting school type as a decisive factor and the study's methodological approach make it more plausible that other factors explain the differences in intervention impact.

    “Taken together, the lack of evidence supporting school type as a decisive factor in intervention effectiveness and our methodological approach make it more plausible that other factors explain the differences in the impact of this intervention found in our study.”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim.

    Premisecitation

    Previous studies suggest that varied kind acts are most effective.

    “varied kind acts are most effective (Sheldon & Lyubomirsky, 2007;Sheldon et al., 2012)”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites Sheldon & Lyubomirsky, 2007

      Not checked in the free run.

    • cites Sheldon et al., 2012

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductnone given

    Authors tasked with statistical analyses were blinded to intervention and control group allocation.

    “Authors tasked with statistical analyses were blinded to the intervention and control group allocation.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim.

    Study design and conductown data

    Multilevel regression models were used to account for the nested data structure of school, classroom, and student.

    “we used two multilevel regression models to consider our nested data structures (school, classroom, and student).”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim.

    Premisecitation

    Research shows that when students build challenging new skills, they may temporarily experience raised anxiety, which dissipates as they master the skills.

    “Research shows that when students build challenging new skills, they may temporarily experience raised anxiety, which then dissipates as they master the skills (Bidell & Fischer, 2016).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites Bidell & Fischer, 2016

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Research suggests that practicing gratitude supports wellbeing, which promotes greater kindness.

    “research suggests that when students practice gratitude, it supports their wellbeing, which ultimately promotes greater kindness (Layous et al., 2013(Layous et al., , 2015) )”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites Layous et al., 2013

      Not checked in the free run.

    • cites Layous et al., 2015

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductreasoning

    Teachers were informed of their classroom's group assignment because they facilitated the intervention.

    “Teachers in the classroom were informed of which classrooms were in the experimental and control groups as they were the main facilitators of the intervention”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim.

    Study design and conductreasoning

    Classrooms were matched into pairs based on similar size, mean age, and proportion of boys and girls before randomization.

    “For the matching process, we aimed to form groups with 1) similar size, 2) similar mean age and 3) similar proportion of boys and girls.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    The vast majority of researched character interventions have used a standardized, one-size-fits-all approach.

    “the vast majority of researched character interventions have used a standardized, one-size-fits-all approach (Brown et al., 2023;Diggs & Akos, 2016;Jakubowski-Tungyoo & Jeynes, 2018;Lavy, 2020).”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites Brown et al., 2023

      Not checked in the free run.

    • cites Diggs & Akos, 2016

      Not checked in the free run.

    • cites Jakubowski-Tungyoo & Jeynes, 2018

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductown data

    The Universidad Internacional de la Rioja's ethics committee approved the study.

    “The study was approved by the Comité de Ética de Investigación from Universidad Internacional de la Rioja.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Study design and conductnone given

    Informed consent was obtained from students in the intervention groups, while passive consent was used for those not undergoing any intervention and without contraindications to questionnaire completion.

    “The project included informed consents for the students in the intervention groups, and passive consents for those who did not carry out any type of intervention and for whom there was no contraindication or problem associated with answering questionnaires.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    A randomized controlled trial showed that preschoolers who participated in a 12-week mindfulness-based kindness curriculum showed improved social competence, including delayed gratification, relative to controls.

    “a RCT showed that preschoolers who participated in a 12-week mindfulnessbased kindness curriculum showed improved social competence, including delayed gratification, relative to controls (Flook et al., 2015).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites Flook et al., 2015

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S2 (checkable). May combine two claims.

    Premisecitation

    More randomized controlled trials on character interventions for students are needed, and there is a particular dearth of randomized controlled trials on kindness interventions for school-aged students.

    “More RCTs on character interventions for students are needed (Berkowitz et al., 2008;Pressman et al., 2015), and there is a particular dearth of RCTs on kindness interventions for school-aged students.”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites Berkowitz et al., 2008

      Not checked in the free run.

    • cites Pressman et al., 2015

      Not checked in the free run.

    • Rests on an assumption: No randomized controlled trials have explored potential gender differences in the impact of kindness interventions.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductnone given

    Participants received full information about the study's goals, methods, and possible risks.

    “For this study, participants were fully informed about the research objectives, procedures, and potential risks.”
    Quote in the paperNot a substantial claim
42 of 42

  • The paper relies on this without support.

    No randomized controlled trials have explored potential gender differences in the impact of kindness interventions.

    “we are not aware of any RCTs that have explored potential gender differences in the impact of kindness interventions”
1 of 1

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • The baseline kindness-recall period changes

    Minor

    The measures section says students were asked about kind acts in the past eight weeks, while both baseline tables label these questions as referring to the last month.

  • English relationship-response counts exceed the sample

    Minor

    The five response counts for the total English sample sum to 264, but Table 1 lists only 198 students in that sample. The control and intervention counts in those rows also exceed their respective group sizes.

    Reported 198 · recomputed 264

  • Spanish sex percentages are reversed in the prose

    Minor

    The prose assigns 49.8% to male students and 50.2% to female students, whereas Table 2 assigns those percentages the other way around.

3 of 3

Cites

Flagged first, then by citations

Research works printed but not linked: 3

  1. Hinton, C., Hill, B., & Yemiscigil, A. (2024). Evidence-based interventions and initiatives to support student well-being in schools. OECD.
  2. Oğuz-Duranand, N., & Kaya-Memiş, A. (2017). An investigation of the relationship between students’ perceived school kindness and school attachment. The Online Journal of Counseling and Education, 6(3), 1–13.
  3. VanderWeele, T. J. (2020). Activities for flourishing: An evidence-based guide. Journal of Positive School Psychology, 4(1), 79–91.

Related

Authors
Hinton, C., de la Rosa Fernández-Pacheco, P. A., Caro Samada, C., Okuzono, S. S., Hill, B., de Gregorio Vicente, O., & Moller, F.
Affiliations
  • Harvard University (US)
  • University of Navarra
  • Universidad Internacional de la Rioja (UNIR)
  • Universidad Internacional de La Rioja
  • Universidad Internacional de La Rioja (ES)
ORCID
Venue
Journal of Moral Education
Publisher
Informa UK Limited
Published
2025-09-11
Pages
1-21
ISSN
  • 0305-7240 (ISSN-L)
  • 1465-3877
DOI
10.1080/03057240.2025.2509821
OpenAlex
W4414143316
Cited by
1
References
56
Citations by year
2026: 1
FWCI
3.13
Type
journal article
Language
en
Open access
Licence
other-oa
Locations
  • Journal of Moral Education (publishedVersion)
  • Re-Unir (International University of La Rioja) (submittedVersion, other-oa)
Funders
  • Universidad Internacional de la Rioja
  • FUNCIVA
  • Proeduca Summa
Topics
  • Social Sciences › Education › Values and Moral Education
  • Social Sciences › Psychology › Social Psychology › Psychological Well-being and Life Satisfaction
  • Social Sciences › Psychology › Social Psychology › Bullying, Victimization, and Aggression
Keywords
gender differences, prosocial behavior, character education, school-based intervention, reflective journals, anxiety, early adolescents, intervention design

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