Differences in academic achievement and cognitive performance
The first aim was to establish whether adolescents who wear traditional uniforms present higher academic and cognitive performance than those who wear sports uniforms. The present findings did not find any significant differences in both educational outcomes.
In line with our findings, a Korean study that explored the link between uniforms and appearance restrictions in middle schools and high schools found no evidence that wearing school uniforms leads to better academic achievement and reported that uniforms would deny the expression of individuality and creativity33. Concerning creativity, it is an essential cognitive resource that is fundamental in the learning processes. In this line, a meta-analysis including 120 studies concludes a significantly stronger relationship between creativity and academic achievement34; thus, traditional uniform wearing could influence both cognitive skills and, in turn, academic achievement. Nonetheless, wearing traditional uniforms also could improve children's discipline, which was associated with a higher academic performance35.
To our knowledge, this is the first study in a sample of Latin-American adolescents exploring both educational outcomes and type of uniform, and the lack of studies related to this topic makes the comparison difficult. Therefore, the present findings contribute to clarifying the scarce and divergent evidence on this matter.6 They also demonstrate that, independently of relevant covariates related to academic and cognitive performance, such as physical fitness, body composition, maturation, and school vulnerability, wearing a traditional uniform was not related to educational outcomes.
Student’s perception and differences in playtime
The second aim was to ask adolescents whether wearing a traditional uniform affects their physical activity, and their answers were compared to playtime according to the type of uniform. Two relevant findings were observed; first, 64.1% of adolescents declared that traditional uniforms affect their physical activity negatively. The second, those who responded affirmatively played 14.5 min more than those who responded negatively. Likewise, a difference of 20 min of playtime was detected in adolescents who responded positively to the question and wore sports uniforms (without statistical significance but ).
In line with the first finding, a study in an Australian primary school found similar results, where 62% of schoolchildren preferred to wear their sports uniform every day and believe they would be more active if they could do so36. Moreover, a study in public middle school students found that 87.3% of them dislike wearing a traditional uniform2. Hence, the present finding from a Latin-American country confirms the opinion of Australian36 and United States2 students contributing to the literature gap in this matter.
Regarding the second finding, the present study highlights two main results, one with a statistical significance (playtime: 14.5 min) and the other without (playtime: 20 min). This has a justification at the public health level relevant to discuss. On the one hand, a study reported significant differences in girls' physical activity levels over boys during breaks and lunch when they wore a sports uniform37. In this line, girls declare that wearing traditional uniforms limits performing physical activities during school time38. These two studies support our findings, but we do not find differences at the sex level, which suggests that both girls and boys in this group of Chilean adolescents could benefit from wearing sports uniforms. On the other hand, adolescents who believe that the traditional uniforms affect their physical activity played 20 min more than those who do not believe so. This non-significant statistical difference could account for a third of the daily physical activity recommendation for children and adolescents39. Although many physical activity interventions in schools have shown modest effects40, small modifications are significant for getting health benefits in real contexts39,40.
Important to highlight is that schools’ principals seem to be a key barrier related to attitudes to changing school uniform policies allowing students to wear sports uniforms every day, but not teachers, parents, and students36. The central concern is that the sports uniform does not fit with ceremonial and formal activities at school. Indeed, in Chile, the school uniform must be agreed upon by principals, teachers, parents and students5; however, the traditional uniform is widely worn. Thus, institutional measures supported by government policies are essential to creating the conditions at the interpersonal level to promote behavioural changes in adolescents.
Therefore, the present findings contribute to the literature showing that promoting a comfortable school uniform could help to increase physical activity in adolescents. Interventional approaches are necessary to corroborate this assumption. Moreover, these findings are useful for future internal school regulations, as well as public policies at educational and health levels due to the prevalence of obesity, physical inactivity, low fitness performance, and educational achievement observed especially in schoolchildren from developing countries41–44.
Bullying and discrimination feelings
The third aim was to compare bullying and discrimination feelings at school according to adolescents’ uniform type. In this sense, the present findings seem contrary to social belief and some studies in this matter2,6, showing similar feelings between groups in both indicators when the model is adjusted for SVI (model 2).
Bullying and discrimination are a global concern at the educational level. For instance, in Chile, 62% of students have reported having been victims of bullying. This percentage is one of the highest percentages based on countries assessed by the Trends in International Mathematics and Science Study − 201145. One central reason is that Chile has one of the highest levels of inequality in Latin America, and its educational system has generated a high level of social segregation among the various types of schools46,47. These economic and social fundamentals have been associated with a greater prevalence of bullying and, in turn, being a bully victim has been negatively correlated with academic and cognitive performance46. However, we cannot establish causality considering bullying as the base of lower educational achievement because there is also the possibility that students who have lower performance choose to bully others46.
In addition, a U.S. study including 6,320 children from a nationally representative sample who were followed from kindergarten entry through the end of fifth grade found that those who wore uniforms did not demonstrate better social behaviour (i.e., social skills, internalising, and externalising behaviour)48. Relevant to note is that their findings were robust even across both public and private schools. Moreover, another study that compared students’ opinions (n = 604) on the benefits of wearing a school uniform after implementing this measure in a public school in Nevada found a potential effect to improve the school climate and students’ experiences. However, students’ beliefs did not support these changes2. In the case of a low-middle-income country (i.e., Mongolia) has reported schoolchildren exclusion feelings when most students wear uniforms in school49.
Finally, and connecting this result with the previous finding addressed, the early detection of bullying and discrimination is fundamental as it could strengthen the social relationships among students and improve school coexistence, where physical activity plays a vital role at school50. Furthermore, increased physical activity has been associated with reduced bullying victimization, enhanced cognitive performance and academic achievement21,51,52. Therefore, in this large sample of Chilean adolescents, the kind of uniform wore was not related to bullying and discrimination, solving great social, family, and school principals’ concerns.
Influence of school vulnerability
Finally, it was hypothesised that possible differences in our analyses would depend mainly on the school vulnerability than the uniform type. This assumption was based on the importance and convergence of factors such as socioeconomics, inequality, and the vulnerability index at the school levels in a Latin-American sample of adolescents16,28,53. Contrary to our hypothesis, model 1 and model 2 seem to be consistent and not affected by the school's vulnerability in academic achievement, cognitive performance, playtime, and bullying.
Nonetheless, discrimination was significantly affected when SVI was not present in the analysis (model 1). In other words, discrimination appreciated by students at schools seems to depend mainly on the social and economic features of the educational establishment and not on the uniform worn. In line with this finding, a study addressing the perceptions of school uniforms with socioeconomic statuses established that students of diverse socioeconomic statuses perceive school uniforms similarly10. In addition, a multilevel study of school violence in 52 countries concluded that income inequality was the main determinant of school violence46. Thereby, future education policies oriented to reduce bullying and discrimination might focus primarily on decreasing social gaps inside and outside the school, and in the specific case of Chile, adolescents' school uniform seems to be not a particular determinant of bullying and discrimination.
Strength and limitations
Some strengths of this study were the large adolescent sample from a usually underrepresented region in this research area and the set of variables included (academic achievement, cognitive performance, playtime, bullying, and discrimination) that contribute to resolving a complex educational topic worldwide. Also, the cognitive performance score based on eight tasks strengthened the study measure. Furthermore, the present statistical analysis permitted control of the effect by cluster and explored a powerful indicator of school vulnerability. Finally, a large group of researchers living in Chile participated and reviewed this study.
Some study limitations were the scarce evidence comparing traditional and sports uniforms and the non- assumption of causality due to the data characteristics. Playtime was evaluated by a self-reported question and not by objective measurement (i.e., accelerometers). Despite the large sample size of adolescents, it is not representative of Chile; hence extrapolations should be made with caution. Finally, the number of schools in each group (traditional or sports uniforms) was different, and schools where adolescents wear sports uniforms do not include any public establishment. In this sense, it is relevant to mention that school type (i.e., administration) has been associated with academic achievements, which could – to a certain extent –-favour schools wearing sports uniforms. In this study, SVI shares variance with the school administration (r = 0.480; p < 0.01), nonetheless SVI is a potent indicator that includes not only the school administration but also other relevant indicators (detailed description in covariates, methods section), being highly related to several variables used in this study16,28,53