Gee, B., Reynolds, S., Carroll, B., Orchard, F., Clarke, T., Martin, D., Wilson, J. and Pass, L. (2020), Practitioner Review: Effectiveness of indicated school‐based interventions for adolescent depression and anxiety – a meta‐analytic review. J Child Psychol Psychiatr, 61: 739-756. doi:10.1111/jcpp.13209.

This systematic review found that school-based interventions for students with some symptoms of anxiety or depression were mildly effective in the short term for the former group and moderately effective in the short term for the latter group.  Effects were greater when interventions were delivered by non-school based staff. 

https://acamh.onlinelibrary.wiley.com/doi/abs/10.1111/jcpp.13209?campaign=woletoc