If he doesn't feel supported, if he just feels pressured, then it's clearly not supporting him at all.
Children should be able to learn and develop at their own pace and not be pressured to attain whatever levels just so that the school can look good on a league table.
Make a nuisance of yourself. Go to your boy's class teacher and ask him/her to remove your son from this class. If they don't. go the head teacher. Keep going - chair of governors, local councillor, local MP - until you get results.
If all else fails, take him out of school and teach him yourself.