The mental health of students is a major issue related to personal and national development. According to the statistics of the World Health Organization (WHO), nearly 20% of the world’s adolescents suffer from different degrees of psychological disorders, which has become a global challenge and an important strategy and priority for the development of public health in various countries [1,2,3] (Kessler et al., 2000; WHO, 2001; WHO, 2000–2011). The initial onset of most mental health problems occurs before the age of 25 [1,4,5] (Kessler et al., 2000; Kelly CM, Jorm AF and Wright A, 2017; Rusch et al., 2011), and the degree of mental health problems is usually mild to moderate. The response to the measures is positive, and the treatment effect is good [6,7,8] (Kessler RC, Avenevoli and Costello J, 2012; Kutcher, 2011; Rutter et al., 2010), if timely identification and intervention during this period can significantly improve the individual Attitudes, behaviors, and mental health levels of seeking professional help [4] (Kelly CM, Jorm AF and Wright A, 2017). However, surveys have shown that 70–80% of adolescents with mental illnesses do not receive the mental health services they need, especially in developing countries [9,10] (Ren Zhihong et al., 2020; Thornicroft, G., 2007). The main reason is the delay of early intervention caused by an insufficient number of full-time and part-time teachers for mental health in schools, low levels of specialization, limited mental health service resources, and low mental health literacy in students [3,10,11,12,13] (WHO, 2011; Thornicroft, 2007; Patel et al., 2007; Tolan and Dodge, 2005; Waddell et al., 2005).

Mental health literacy is the knowledge, beliefs, and behaviors about mental disorders, including understanding how to achieve and maintain positive mental health, understanding mental disorders and their treatment, reducing the stigma associated with mental disorders, and improving self-help and helping others [14,15,16,17] (Jorm et al., 1997; Jorm, 2012; Kutcher, Bagnell and Wei Y, 2015; Kajawu et al., 2016). At present, there are two main ways to measure mental health literacy: case interviews and questionnaire surveys [9] (Ren zhihong et al., 2020). Jorm et al. (1997) used case interviews to investigate public awareness of the causes and risk factors of depression and schizophrenia [14]. There are various forms of questionnaires, but no questionnaire has been widely used at present [9] (Ren zhihong et al., 2020). Improving mental health literacy has been widely recognized by countries and international organizations as the key to promoting individual mental health. Due to a lack of mental health knowledge, limited ability to identify mental disorders, and the impact of mental illness stigma, students are less willing to seek formal help, so they are more dependent on others for help to identify mental illness symptoms and guide them to appropriate interventions, such as friends, family, teachers, etc. Among them, teachers, as the adults with the most contact with students’ campus life, have unique advantages in identifying, helping, and supporting students’ mental health [18,19,20] (Atkins et al., 2011; McGorry et al., 2011; Rowling, 2015).

In the past two decades, many countries have carried out evidence-based intervention projects based on the participation of ordinary schoolteachers and focusing on improving students’ mental health literacy (MHL) as an important strategy and approach to identifying early symptoms in adolescents, reducing stigma, and improving the effectiveness of help-seeking [21]. These projects included the Adolescent Mental Health First Aid Program (United States) [22] (Theda Rose et al., 2017), Mental Health Teaching Program (United Kingdom) [23] (Paul B et al., 2009), National Curriculum for Personal Development, Health and Physical Education (Australia) [24] (Yael Perry et al., 2014), Middle School Students’ Knowledge, Attitudes and Help for Depression (Hong Kong, China) [25] (Eliza s et al., 2016). Teachers use videos in the classroom to let students contact mental health patients, teach mental health knowledge and classroom seminars, and achieve other means to increase students’ mental health knowledge, reduce stigma, and promote a help-seeking willingness and actual help-seeking behavior. However, the experimental results are different. For example, in the intervention of mental health knowledge, Stan Kutcher (2015) and Alan Mcluckie (2014) [16,26] measured immediately after the experiment and showed that school mental health knowledge improved to a significantly large effect size (p < 0.001, d ≥ 0.8). However, Amanda J. Nguyen (2020) showed a significantly small effect size (p < 0.001, d ≤ 0.2) immediately after the students’ mental health knowledge intervention trial [27], making it difficult for people to accurately grasp whether the mental health courses provided by ordinary teachers can effectively improve the students’ mental health literacy and the improvement effect. In addition, the existing meta-analysis has some limitations. For example, Yifeng Wei (2013) et al. systematically reviewed a total of 27 school-based mental health literacy programs with participants aged 12–25 [28], but this meta-analysis was not aimed at teacher-led projects. Ordinary teachers refer to teachers who are not full-time mental health teachers or part-time mental health teachers in schools. The intervention project led by ordinary teachers can make all teachers participate in school mental health education projects and effectively alleviate the shortage of teachers in school mental health education.

2. Description of Included Studies

3. Studies on Evidence-Based Intervention

3.1. Publication Bias and Heterogeneity Testing

3.2. Main Effects and Sensitivity Tests