The average age in grade one of these students was 5.4 years increasing on average with one year per grade to reach 15 years in grade 10. In most grades boys are/were slightly older than girls, except for grade eight and nine where girls are older. For boys, the standard deviation increases slightly from grade 8 onwards, whereas for girls the standard deviation doubles from grade 8 onwards. In other words, from grade 8 onwards, there is much more variation in age among, especially, the girls.
2. Average age by grade and gender
6