Table 2 Study characteristics for intervention studies

Blossom et al. (2020) [41]

Intervention: 241 (61.8%),Control: 256 (64.5%), Youth with elevated depression, USA

Intervention at T1

T2: 3 months later (8th grade)

T3: 9 months later

T4: 12 months later

T5: 1.5 yrs later (9th grade)

Randomised controlled trial: 5 waves; Baseline, 3-month follow-up (school attachment), 9-month follow up (self-esteem) and 18-month follow-up (outcomes)

School attachment (High School Questionnaire); Depression (Short Mood and Feelings Questionnaire)

HSTP: aimed to reduce risks of depressive symptoms among students transitioning to high school by increasing self-esteem and school attachment through providing them with social support (both at school and with caregivers) and promoting students’ participation in positive, school-based activities (A one-on-one standardized interview and clinical follow-up with a trained clinician, with a telephone call to parents to review concerns and to make recommendations for additional services as needed)

School attachment at T2 did not mediate the effects of the HSTP intervention on depressive symptoms at T5 (95% CI = 0.03 to 0.04). Sequential mediation model: HSTP intervention influenced school attachment at T2 which contributed to self-esteem at T3, which in turn contributed to lower depressive symptoms at T5 (95% CI = 0.02 to 0.0005). After accounting for self-esteem the direct effects of the intervention and T2 school attachment on T5 depressive symptoms were not significant (B = .02, p = .79). A second mediation model where the HSTP intervention predicted T3 school attachment, which predicted T4 self-esteem, which in turn predicted T5 depression was also significant (95% CI = 0.04 to 0.003)

Singla et al. (2021) [42]

Intervention: 2854 (53%), Control: 2685 (52%), India

Intervention: 13.70 (95% CI = 13.67–13.73)

Control: 13.71 (95% CI = 13.68–13.74)

T2: 8 months later

T3: 17 months later

Subset of larger randomised controlled trial: 3 waves; Baseline, 8-month follow-up, and 17-month follow-up

Relationship to school and school belongingness (subscales of Beyond Blue School Climate Questionnaire); Depression (Patient Health Questionnaire-9)

SEHER: In addition to the information provided to the control arm, the intervention emphasized the importance of a positive school climate (supportive relationships between school community members, a sense of belonging to the school, a participative school environment) by identifying several areas for action (e.g., promoting social skills among adolescents) (Trained teacher in each school who conducted classroom-based sessions on life skills, including developmental changes, developing positive and responsible relationships, gender and sexuality, prevention of HIV and other sexually transmitted infections, and substance use)

Relationships at school 8 months post randomization mediated the association between the intervention and depressive symptoms 17 months post randomization (X- > M: standardized beta = 1.116 [0.20], M—> Y: standardized beta = -0.064 [0.017]). Indirect effect: -0.071 (-0.098 to 0.036). School belongingness 8 months post randomization did not mediate the relationship between intervention status and depressive symptoms 17 months post randomization (X- > M: standardized beta = 0.878 [0.22], M—> Y: standardized beta = 0.029 [0.016]); X- > M (effect of independent variable on mediator) M- > Y (effect of mediator on dependent variable)