Table 1.

Descriptive Statistics.

	Ages 8–10 (M = 9.22, SD = .88)				Ages 11–16 (M = 13.36, SD = 1.72)				Standard. LV Loadings
	n	Mean	SD	Skew	n	Mean	SD	Skew
Working Memory Latent Variable
Digit Span (Raw)	720	11.29	3.02	.34	601	14.58	3.53	.50	.65
Sentence Span (Raw)	718	4.32	1.70	.61	598	6.46	2.25	.57	.64
Counting Span (Raw)	719	5.77	2.23	.50	598	7.88	2.33	.29	.69
Inhibition Latent Variable
CPT Vigil. Errors (Raw)~ag	713	6.81	6.27	1.68	594	2.99	4.13	3.11	.49
CPT Distract Errors (Raw)~ag	640	13.95	9.93	.74	559	6.31	6.92	1.71	.51
SSRT Version 1 (Raw)~bg	389	344.44	119.89	.75	390	262.37	86.68	1.44	.51
SSRT Version 2 (Raw)~bg	297	405.36	142.15	.46	203	275.21	102.29	1.47
Processing Speed Latent Variable
CO Perceptual Speed (Raw)	719	13.40	5.53	.66	602	26.28	8.52	.54	.85
Identical Pictures (Raw)	720	47.29	11.06	.33	602	70.03	14.00	.12	.67
Naming Speed Latent Variable
RAN Color (Raw)	720	19.88	4.19	.29	602	26.23	5.19	.32	.77
RAN Object (Raw)	720	17.54	3.21	−.02	602	21.55	3.50	.00	.55
Listening Comprehension Latent Variable
WJ Oral Comp. (SS)	716	107.94	11.59	−.18	602	105.23	10.14	−.23	.75
Barnes KNOW-IT- Literal (Proportion)~c	717	0.77	0.21	−.83	601	0.83	0.18	−1.28	.53
Barnes KNOW-IT- Coher. (Proportion)~c	716	0.73	0.19	−.76	600	0.82	0.16	−1.27
Barnes KNOW-IT- Infer. (Proportion)~c	717	0.75	0.18	−.83	599	0.80	0.16	−1.40
QRI Listen- Recall (Raw)d	713	0.34	0.16	.54	596	0.30	0.12	.37	.62
QRI Listen- Questions (Raw)d	718	4.47	1.39	−.78	602	4.38	1.13	−.90
Reading Comprehension Latent Variable
QRI Read- Recall (Raw)e	702	0.36	0.15	.16	593	0.29	.13	.87	.64
QRI Read- Questions (Raw)e	708	4.46	1.18	−.76	599	4.61	0.96	−.68
GORT (Scaled)	706	10.58	3.06	.21	594	11.89	3.27	.31	.71
PIAT Comp. (SS) f	714	109.05	13.04	−.47	593	103.94	12.47	−.34	.39/.48f
WJ Pass. Comp. (SS)f	715	101.10	10.67	−.17	601	102.75	10.40	.10	.54/.33f
Word Reading Latent Variablef
Word Recognition (Raw)	720	88.98	37.37	−.01	602	144.93	34.83	−.63	.89
PIAT Read. Rec. (SS)	714	106.74	12.20	−.31	593	102.79	11.99	−.14	.89
PIAT Spelling (SS)	714	105.16	12.32	−.08	594	100.36	13.44	.15	.77

Note: Variables that share superscripts ^a to ^ewere combined together for all subsequent analyses;

^fWJ Passage Comprehension and PIAT Reading Comprehension cross-loaded onto the Word Reading Latent Variable;

^gall inhibition tasks were reverse-coded for all subsequent analyses, such that larger values correspond to better performance.

Standardized latent variable loadings (Stand. LV Loadings) come from phenotypic confirmatory factor analyses done on one twin per pair selected at random.

^~Due to significant skew, the variable was transformed prior to all analyses.