. Author manuscript; available in PMC: 2011 Feb 1.

Published in final edited form as: J Educ Psychol. 2010 Feb 1;102(1):32–42. doi: 10.1037/a0017288

Table 3.

Intraclass Correlations for Change Scores for Same- and Different-Class Twins Pairs (N Pairs in Parentheses; Contrasts Significant at .01 in Bold)

Grades	Test	MZ pairs		DZ pairs

		S	D	S	D
K - 1		(152, 189)		(141, 201)
	Spelling^a	.70	.54	.45	.50
	TOWRE SWE	.72	.69	.46	.51
	TOWRE PDE	.65	.64	.45	.40
1 - 2		(114, 168)		(86, 190)
	TOWRE SWE	.53	.57	.39	.29
	TOWRE PDE	.46	.43	.29	.30
	WRAT Spelling	.38	.45	.27	.20
	WPC	.38	.31	.32	.07

Note: S = Same class, D = Different class, TOWRE SWE = Test of Word Recognition Efficiency, Sight Word Efficiency; TOWRE PDE = Test of Word Recognition Efficiency, Phonemic Decoding Efficiency; WRAT Spelling = Wide Range Achievement Test, Spelling; WPC = Woodcock Reading Mastery Test (Revised), Passage Comprehension.

In kindergarten the children were assessed with our own spelling test and in Grade 1 with the WRAT Spelling.