Table 3. Summary of findings (random effects model).

Includes size of effects, heterogeneity, quality of evidence (GRADE) and conclusion about the certainty of each outcome.

Outcome (self-concept)	Studies	Sample size	Random effects model			Heterogeneity				GRADE	Certainty of outcome
			SMD (95% CI)	Z	P	Chi2	df	P	I2
Primary Outcome
Average	13	3,348	−0.57 [−0.81 to −0.33]	4.65	<.001	55.66	12	<.001	78	Medium	Probable moderate association
Secondary Outcomes
Reading-Spelling -Writing	5	2,002	−1.03 [−1.66, −0.41]	3.23	<.001	41.69	4	<.001	90	Low	Possible large association
Academic	7	2,595	−0.67 [−0.97, −0.36]	4.26	<.001	21.84	6	.001	73	Low	Possible moderate association
Math	4	1,899	−0.64 [−1.03, −0.24]	3.17	.002	10.89	3	.01	72	Low	Possible moderate association
Global	9	2,046	−0.57 [−0.87, −0.28]	3.79	<.001	37.21	8	<.001	78	Low	Possible moderate association
Behavioural	2	177	−0.32 [−0.62, −0.03]	2.15	.03	0.07	1	.78	0	Low	Possible moderate association
School	2	910	−0.28 [−1.29, 0.74]	0.05	.59	7.26	1	.007	86	Low	Unlikely moderate association
Physical Appearance	3	213	−0.28 [−0.55, −0.01]	2.03	.04	1.43	2	.49	0	Low	Possible moderate association
Work	1	36	−0.23 [−0.89, 0.42]	0.70	.48					Low	Unlikely moderate association
Social	5	869	−0.15 [−0.34, 0.04]	1.57	.12	4.33	4	.36	8	Low	Unlikely small association
Athletic	2	177	0.15 [−0.15, 0.44]	0.98	.33	0.92	1	.34	0	Low	Unlikely small association
Home	1	1,804	0.31 [−0.29, 0.91]	1.01	.31					Low	Unlikely moderate association