Table 1 Baseline characteristics of the five grades analyzed

4th grade

5th grade

6th grade

7th grade

8th grade

(9 - 10 years)

(10 - 11 years)

(11 - 12 years)

(12 - 13 years)

(13 - 14 years)

9.7 ± 0.5

10.7 ± 0.5

11.7 ± 0.5

12.6 ± 0.5

13.4 ± 0.5

16/16

15/10

16/10

16/9

0/10