Background. The high prevalence of mental disorders in early adolescents, and its consequences, encourage the need for validated instruments to identify and assess psychosocial problems. Objectives: i) To evaluate the psychometric properties of the Pediatric Symptom Checklist (PSC) questionnaires (PSC-Y, 35 items, and PSC-17-Y) and its subscales (Attention, Internalizing and Externalizing subscales), including the assessment of the item structure, concurrent validity, and reliability; and ii) To assess possible associations between bullying experiences, school climate and school membership with psychological problems identified by the PSC questionnaire. Methods: A cross-sectional study was carried out in 39 schools in Santiago of Chile. The sample consisted of 3,968 adolescents aged between 10 and 11 years. Descriptive analysis of the Pediatric Symptom Checklist was performed along with measures of dimensionality, reliability, and correlations with a validated questionnaire exploring similar constructs, the Strengths and Difficulties Questionnaire. Finally, associations of bullying, school climate, and school membership with the three subscales of the PSC were explored. Results: Both versions of PSC had problems with item #7 (Act as if driven by motor), which did not load in any of the latent factors. It was removed from later analyses. The three-factor structure of PSC was confirmed. All remaining items had high factor loadings in their corresponded latent factors, and the reliably was high for the total scales (PSC-34-Y, ω=0.78; PSC-16-Y, ω=0.94) and for the subscales of PSC-16-Y (Attention, ω=0.77; Internalizing, ω=0.79; Externalizing, ω=0.78). The goodness of fit was adequate, and the correlation between PSC subscales and SDQ subscales was high. Victimization and perpetration were associated with all PSC subscales, and higher school climate and stronger school memberships were negatively associated with PSC symptoms. Conclusions: The current findings seem to demonstrate that the PSC is a valid and reliable instrument to identify and assess psychosocial problems in early adolescents.Background. The high prevalence of mental disorders in early adolescents, and its consequences, encourage the need for validated instruments to identify and assess psychosocial problems. Objectives: i) To evaluate the psychometric properties of the Pediatric Symptom Checklist (PSC) questionnaires (PSC-Y, 35 items, and PSC-17-Y) and its subscales (Attention, Internalizing and Externalizing subscales), including the assessment of the item structure, concurrent validity, and reliability; and ii) To assess possible associations between bullying experiences, school climate and school membership with psychological problems identified by the PSC questionnaire. Methods: A cross-sectional study was carried out in 39 schools in Santiago of Chile. The sample consisted of 3,968 adolescents aged between 10 and 11 years. Descriptive analysis of the Pediatric Symptom Checklist was performed along with measures of dimensionality, reliability, and correlations with a validated questionnaire exploring similar constructs, the Strengths and Difficulties Questionnaire. Finally, associations of bullying, school climate, and school membership with the three subscales of the PSC were explored.

The inclusion criteria of the participating schools were the following: (1) Schools that have 5th -6th grades, (2) mixed schools, (3) located in Santiago city, (4) having two classes per grade, and (5) High vulnerability (>75%) measured by the Chilean index School Vulnerability Index-National System of Equality Allocation (IVE-SINAE). This index is built every year by the Ministry of Education of Chile and assigned to every school based on poverty conditions such as poor health, low family income, receiving state benefits, and the risk of school failure of the students. In other words, the IVE-SINAE index shows the proportion of students in a school who are in most need. The study population consisted of students attending 5th or 6th grade (ages 10-11) from a total of 39 schools located in Santiago, Chile. The data was collected in November 2017 in accordance with the Declaration of Helsinki, with the approval of the ethics committee of the Universidad de los Andes (January 18th, 2016). First, school authorities were informed about the study aims, methods, and assessments, and afterward, they agreed to participate. Second, an informed and written consent form was sent to the parents or main caregivers in order to accept the participation of the students. Finally, informed and written assent was also provided from all students. The questionnaires were responded by students in the classroom, under the supervision of a research assistant who was previously trained to administer the questionnaire and answer questions from students. All questionnaires were self-reported. Once completed the questionnaires were introduced in a sealed envelope and later, the research assistant entered the data in a excel sheet. The entries were reviewed by the research coordinator and the mistakes were corrected. The questionaries were stored in a secure storage. Only Principal investigator and research coordinator have access to the physical storage. A total of 4,495 students were eligible to participate and were invited. Of these, a total of 3,968 (88.3%) consented and responded to the questionnaire.