Whole School SEND (WSS) Review: study protocol for a two-arm pragmatic parallel cluster randomised controlled trial in 160 English secondary schools

Table 2 Sample size calculations (calculated using PowerUp!^a)

	All pupils	SEND pupils	FSM pupils
Minimum Detectable Effect Size (MDES)	0.19	0.20	0.19
Pre-test / post-test correlations
Level 1 (pupil)	0.70	0.70	0.70
Level 2 (class)	n/a	n/a	n/a
Level 3 (school)	0.32	0.32	0.32
Intracluster correlations (ICCs)
Level 2 (class)	n/a	n/a	n/a
Level 3 (school)	0.20	0.20	0.20
Alpha	0.05	0.05	0.05
Power	0.80	0.8	0.8
One-sided or two-sided?	Two	Two	Two
Average cluster size	180	25	42
Number of schools
Intervention	80	80	80
Control	80	80	80
Total	160	160	160
Number of pupils
Intervention	14,400	2000	3360
Control	14,400	2000	3360
Total	28,800	4000	6720

ISSN: 1745-6215