Table 1.

Means and SDs of memory components.

	Grade 3		Grade 4
Variable	M	SD	M	SD	ta	pb
Verbal short-term memory (STM)	4.55	0.73	4.92	0.73	-4.68	<0.001
Verbal working memory (WM)	2.89	0.60	3.30	0.55	-4.72	<0.001
Visuo-spatial STM	5.06	0.70	5.56	0.67	-4.88	<0.001
Visuo-spatial WM	4.18	1.10	4.69	0.86	-3.82	<0.001

^aPaired sample t test. ^bTwo-tailed significance level of 0.01.