TABLE 1.

Sample data.

Grade	n	Mean age (SD)	Boys	Girls
1° grade	58	6.31 (SD = 0.63)	32 (55.17%)	26 (44.83%)
2° grade	56	7.34 (SD = 0.59)	31 (55.36%)	25 (44.64%)
3° grade	62	8.41 (SD = 0.58)	30 (48.39%)	32 (51.61%)
4° grade	64	9.21 (SD = 0.64)	33 (51.56%)	31 (48.44%)
5° grade	60	10.32 (SD = 0.54)	26 (43.33%)	34 (56.67%)
6° grade	59	11.15 (SD = 0.66)	30 (50.85%)	29 (49.15%)
Total	359	8.79 (SD = 1.81)	182 (50.7%)	177 (49.3%)