Table 8.

Cluster robust meta‐regression for treatment duration (weeks) for academic effect sizes.

Effect	Hedges’ g	95% CI of g	df	p
Intercepta	0.188	(−0.045, 0.420)	9.13	0.101
Within‐study effect by week	0.007	(−0.087, 0.100)	1.00	0.538
Between‐study effect by week	0.002	(−0.005, 0.009)	2.36	0.353

Note: N of studies = 18, N of effect sizes = 67, assumed ρ = 0.8, I ² = 80.72. Cluster robust estimates with df < 4.00 should be interpreted with caution (Tanner‐Smith, Tipton, & Polanin, 2016). Positive effect sizes favor Montessori over traditional education.

Abbreviation: CI, confidence interval.

^a Reference category/intercept.