if he's just started school, it's probably not a good time to start this.
My DS was dry most nights with the odd accident, but after starting school last september he regressed pretty rapidly and is still in pyjama pants now. We've tried getting him up at all hours, but nothing seems to work.
HV says its normal and they will only consider it a problem if he gets to seven.
I'd leave it for a while. Not an expert, so perhaps a HV will come along and correct me if I'm wrong, but night time dryness is different to daytime. My DS was very late, and ended up with an alarm. GP and HV wouldn't do anything til he was 7, as already said, up to 7 is considered normal. I was told that there are 2 main factors: 1) waking up when you need a wee 2) apparently some kind of hormone kicks in at some point which reduces the amount of urine produced while we sleep. If he's really not ready, you're heading for a lot of washing and a frustrated child. I agree that just after starting school is not a good time to do this. You might however sit him down and have a chat about it, there's every chance it'll come out accidentally at school that he's not dry yet or a play-date will find his nappies/pull-ups. Just explain that it's not the same as wearing a nappy during the day, and there will be lots of other children in his class in the same boat.
Myself, a friend and my sister in law, we all just left it. Didn't say anything and waited until the nappies were dry at night. Then took them off. This was completely pain free. My daughter and my nephew were dry at night before they were 3, my friends daughter took much longer, she was almost 4. Good luck
my ds was 4.5 when I got rid of his nappies at night. He was always soaking wet in the morning-but it transpired that he would wake-climb out of bed-stand with his legs apart and wee in his nappy before climbing back into bed-I decided that if he could do that he could go to the loo. He has never had an accident (now 6)
So try and feel his nappy before he wakes n the morning if possible as a wet nappy in the morning doesn't necessarily mean that he cannot go through.