Comparison 1. Diet quality.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1.1 Diet quality	6	1973	Std. Mean Difference (IV, Random, 95% CI)	0.34 [0.04, 0.65]
1.2 Diet quality (sensitivity: studies at low overall risk of bias)	3	957	Std. Mean Difference (IV, Random, 95% CI)	0.21 [‐0.03, 0.45]
1.3 Diet quality (Health Promoting Schools: curriculum versus no curriculum)	6	1973	Std. Mean Difference (IV, Random, 95% CI)	0.34 [0.04, 0.65]
1.3.1 Curriculum	2	639	Std. Mean Difference (IV, Random, 95% CI)	0.10 [‐0.11, 0.32]
1.3.2 No curriculum	4	1334	Std. Mean Difference (IV, Random, 95% CI)	0.46 [0.08, 0.84]
1.4 Diet quality (SES: low versus high/unclear)	6	1973	Std. Mean Difference (IV, Random, 95% CI)	0.34 [0.04, 0.65]
1.4.1 Low	3	834	Std. Mean Difference (IV, Random, 95% CI)	0.30 [0.16, 0.44]
1.4.2 High/unclear	3	1139	Std. Mean Difference (IV, Random, 95% CI)	0.40 [‐0.22, 1.01]
1.5 Diet quality (intervention modality: included face‐to‐face, telephone and online delivery versus did not include face‐to‐face, telephone and online delivery)	6	1973	Std. Mean Difference (IV, Random, 95% CI)	0.34 [0.04, 0.65]
1.5.1 Included face‐to‐face, telephone and online delivery	4	1334	Std. Mean Difference (IV, Random, 95% CI)	0.46 [0.08, 0.84]
1.5.2 Did not include face‐to‐face, telephone and online delivery	2	639	Std. Mean Difference (IV, Random, 95% CI)	0.10 [‐0.11, 0.32]
1.6 Diet quality (intervention delivery personnel: included healthcare professionals versus did not include healthcare professionals)	6	1973	Std. Mean Difference (IV, Random, 95% CI)	0.34 [0.04, 0.65]
1.6.1 Included healthcare professionals	4	1334	Std. Mean Difference (IV, Random, 95% CI)	0.46 [0.08, 0.84]
1.6.2 Did not include healthcare professionals	2	639	Std. Mean Difference (IV, Random, 95% CI)	0.10 [‐0.11, 0.32]