Does Watford Grammar School take more pupils in year 9.

Only if a child leaves and there is a space, but that can happen any year. My son's class had 2 or 3 leave and some new joiners over the 5 years. One child left in year 9 after taking 13+ at a private school. Similar story at the girls school. There have been a few kids leaving and then new starters taking their place in different years.