Table 1.

Descriptive analyses of the participants across the four time points

Time point	Academic year	Number of participants	Mean age (SD)
Time 1	2009/10	3328	12.59 (.743)
Time 2	2010/11	2905	13.59 (.697)
Time 3	2011/12	2668	14.54 (.680)
Time 4	2012/13	2427	15.49 (.656)