Table 1.

Means and Standard Deviations of W-Scores and Raw Scores, Estimates of Heritability and Shared Environment, and Results of Significance Tests for Each Measure at Each Assessment Point

	W score		Raw		h2	c2
	M	SD	M	SD
WRMT: Word Identification
Assessment 1	386.56	40.1	15.3	17	0.2*	0.74*
Assessment 2	438.31	37.27	39.6	19	0.33*	0.6*
Assessment 3	470.73	29.11	56.7	15	0.4*	0.5*
Assessment 4	495.81	20.88	70.2	11	0.59*	0.25*
Assessment 5	506.31	17.32	76.1	9	0.66*	0.15 ns
Assessment 6	514.09	15.1	80.6	8	0.82*	0 ns
WRMT: Word Attack
Assessment 1	457.84	19.66	5.3	7	0.3*	0.58*
Assessment 2	481.15	18.77	15.3	10	0.27*	0.52*
Assessment 3	495.19	16.18	23.4	10	0.58*	0.23 ns
Assessment 4	504.41	14.29	29.2	8	0.75*	0 ns
Assessment 5	509.21	13.51	31.8	7	0.47*	0.24 ns
Assessment 6	510.88	11.94	32.9	6	0.71*	0.01 ns
CTOPP: Rapid Naming
Assessment 1	—	—	382.02	31	0.51*	0.25 ns
Assessment 2	—	—	355.39	21	0.61*	0.22 ns
Assessment 3	—	—	343.75	13	0.44*	0.3*
Assessment 4	—	—	335.59	9	0.31*	0.33*
Assessment 5	—	—	331.41	7	0.69*	0.02 ns
Assessment 6	—	—	328.71	6	0.45*	0.26 ns
WRMT: Reading Comprehension
Assessment 1	448.37	20.18	11.01	9	0.39*	0.39 ns
Assessment 2	469.41	20.61	21.47	10	0.44*	0.47*
Assessment 3	486.97	17.2	31.01	9	0.32*	0.5*
Assessment 4	500.6	13.99	38.44	7	0.72*	0.05 ns
Assessment 5	508.24	11.83	42.68	6	0.55*	0.23 ns
Assessment 6	513.92	12.47	45.97	7	0.82*	0 ns

Note. WRMT = Woodcock Reading Mastery Test; CTOPP = Comprehensive Test of Phonological Processing; h² = proportion of raw-score variance attributable to heritability; c² = proportion of raw-score variance attributable to shared environment. Mean ages at Assessments 1–6 were 6.1, 7.2, 8.2, 9.8, 10.9, and 12.1.

^*p < .05.