A total of 8,219 students participated in the MHSC questionnaire and 7493 qualified questionnaires eventually returned, with a gender distribution of 3702 males and 3791 females. Among them, 2140 students were found to have psychological problems, with a detection rate of 28.6% (95% CI 27.5–29.6). The prevalence rate of girls (31.9%, 95% CI 30.4–33.4) was significantly higher than that of boys (25.1%, 95% CI 23.8–26.5) (χ2 = 41.736, p < 0.01; Table 1). Furthermore, as shown in Table 1, the prevalence rate was 23.5% (95% CI 21.9–25.0) for 12–13 years, 29.8% (95% CI 28.2–31.4) for 14–15 years and 36.9% (95% CI 34.2–39.5) for 16–18 years, and there was a statistically significant difference in the detection rate of metal disorders by age group (χ2 = 82.768, p < 0.01).

Of the 7493 students, 2140 participants with MHSC positive and 1000 participants with MHSC negative were included in the secondary interview. A total of fourteen types of mental disorder were diagnosed in 930 children through the MINI-KID and DSM-IV interview. Among these mental disorders, obsessive compulsive disorder (OCD) had the highest prevalence (9.1%, 95% CI 8.4–9.7), followed by major depressive disorder (MDD; 8.9%, 95% CI 8.3–9.6), anxiety disorders (AD; 4.8%, 95% CI 4.3–5.3), attention–deficit hyperactivity disorder (ADHD; 2.5%, 95% CI 2.1–2.8), oppositional defiant disorder (ODD; 1.9%, 95% CI 1.6–2.2) and sleep disorder (SD; 1.9%, 95% CI 1.6–2.2) (Table 2).

As shown in Table 3, the overall point prevalence rate for boys was 10.8% (95% CI 9.8–11.7) lower than the 14.0% (95% CI 12.9–15.1) for girls. Compare to boys, the prevalence of the MDD, AD, OCD, SD, bulimia nervosa (BN) and anorexia nervosa (AN) was significantly higher in girls, at 10.0% (OR 0.763), 5.5% (OR 0.720), 10.0% (OR 0.797), 2.3% (OR 0.599), 1.4% (OR 0.112) and 0.3% (OR 0.157), respectively. However, prevalence rates for ADHD, tic disorder (TD), substance use disorder (SUD) and mania or hypomania (MA) were higher for boys, at 3.5% (OR 2.447), 1.5% (OR 4.749), 1.5% (OR 9.338) and 0.8% (OR 4.416), respectively. There was no gender difference in the risk of ODD, social phobia (SOP), post-traumatic stress disorder (PTSD) and psychotic disorder (PD) (p > 0.05).

It is noteworthy that the prevalence of overall mental disorders increases with age, as shown in Table 4. The prevalence of mental disorders was upwards of 20% in the 17–18-year-old age group relative to other age groups (21.9%, 95% CI 17.7–26.2 and 21.8%, 95% CI 13–30.7, respectively), while the lowest prevalence in the 12-year-old age group at less than 10% (8.7%, 95% CI 6.9–10.4). The prevalence of MDD and anxiety disorders was highest among participants aged 18 years (18.4%, 95% CI 10.1–26.7 and 10.3%, 95% CI 3.8–16.9, respectively), and the prevalence of OCD, SD and SUD was highest among participants aged 17 years (20.5%, 95% CI 16.4–24.7, 3.0%, 95% CI 1.3–4.8 and 3.0%, 95% CI 1.3–4.8, respectively). Inconsistently, the younger the age, the higher the risk of ADHD, ODD and TD, with prevalence rates of 5.2% (95% CI 3.8–6.6), 3.5% (95% CI 2.3–4.6) and 3.3% (95% CI 2.1–4.4), respectively, in the 12-year-old group (Table 4).

Comorbidities of the several common mental disorders are shown in Table 5. Individuals diagnosed with MDD, AD, OCD and SD had higher rates of comorbidity. MDD was most frequently comorbid with AD (32.8%), OCD (32.5%), and SD (20.0%) in 220, 218, and 134 individuals, respectively. The most common comorbidity of ADHD was AD (29.9%), ODD was ADHD (26.9%), TD was MDD (35.9%) and SUD was SD (28.3%).