Table 1.

Children's scores on control measures at each measurement time.

	Cohort 1
	T1, Grade 2, N = 59, 28 girls			T2, Grade 3, N = 60, 28 girls			T3, Grade 4, N = 57, 27 girls
Control measure	M	SD	Range	M	SD	Range	M	SD	Range
Age (years;months)	7;6	0.4	7;1–8;7	8;6	0.4	8;1–9;7	9;5	0.4	9;1–10;7
Non-verbal IQ	−0.32	0.95	−2.00–1.33	—	—	—	—	—	—
Vocabulary	0.38	1.32	−2.00–3.40	—	—	—	—	—	—
Spelling accuracy	−0.66	1.15	−3.84–1.14	−0.32	0.80	−1.84–1.43	−0.86	1.12	−4.32–1.65
Word reading	0.48	0.68	−0.80–2.29	0.57	0.78	−1.02–2.34	0.55	0.89	−1.51–2.08
Handwriting quality	−0.54	1.00	−2.75–1.43	−1.09	1.24	−3.8–1.89	−1.13	1.61	−3.86–2.14
Handwriting speed	0.19	0.85	−1.47–2.20	0.41	1.00	−1.32–2.59	0.26	0.88	−1.08–2.05
	Cohort 2
	T1, Grade 3, N = 55, 28 girls			T2, Grade 4, N = 56, 28 girls			T3, Grade 5, N = 53, 26 girls
Control measure	M	SD	Range	M	SD	Range	M	SD	Range
Age (years;months)	8;7	0.4	8;0–9;8	9;7	0.4	9;0–10;7	10;6	0.4	10;0–11;7
Non-verbal IQ	0.12	0.93	−2.00–2.33	—	—	—	—	—	—
Vocabulary	0.87	0.94	−1.78–3.20	—	—	—	—	—	—
Spelling accuracy	−0.15	0.87	−2.56–1.55	−0.49	1.06	−4.23–1.34	−0.79	1.16	−3.47–1.34
Word reading	0.61	0.88	−0.83–2.89	0.65	0.88	−0.84–2.51	0.97	2.82	−1.37–1.98
Handwriting quality	−0.91	1.62	−5.16–1.89	−0.66	1.58	−4.43–3.57	−0.76	1.72	−6.83–2.03
Handwriting speed	0.74	1.03	−1.70–4.67	0.46	0.93	−1.47–3.05	0.84	0.86	−0.98–3.22

The scores presented in this table are z-scores calculated by comparing children's raw scores to the clinical tests' norms for their age or grade (see Measures section for more details). These scores have a mean of 0 and a standard deviation of 1. They allow positioning children's performances in comparison to the average performances for their age or grade. Z-scores below −2 SD indicate pathological performances, and scores below −1.5 SD indicate low performances. Conversely, scores above +2 SD indicate exceptionally high performances.