Whether your child is starting school for the first time or entering his last year of high school, one thing that many children have to deal with is getting on a good sleep schedule. Not getting enough sleep is an important cause of school performance problems, leading to attentional and behavioral problems, so it is important to encourage good sleep habits for children of all ages.
For younger children who are still taking naps and are starting a full day kindergarten, the adjustment in their sleep habits can be almost as big as the whole issue of starting school.
If you figure that the average 5 year old needs about 11 hours of sleep in a day, if your child was taking a 1 or 2 hour nap during the day and only sleeping 9 or 10 hours at night, you now have to shift the whole 11 hours to nighttime. Making this shift in his sleep routine can be hard and you will likely have a few days where he is overtired and irritable.
Your first step is going to be having him give up his nap. If he is used to sleeping in, you will also have to begin waking him up earlier. Doing both of these steps around the same time in a cold turkey approach is probably better than a more gradual approach of shorter naps, etc.
Lastly you will have to get him used to going to bed earlier.
Giving up his nap time and waking him up earlier might not be too hard, but shifting to an earlier bedtime may take some doing. A gradual approach of moving his bedtime 10-15 minutes earlier every few days is usually easier than making a big jump of an hour or two. For example, if your child usually takes a two hour nap and goes to sleep at 10pm and wakes up at 7am, you might want to have hime give up the nap and then have him go to bed at 9:45pm and then 9:30pm, etc. until you get to an 8pm bedtime.
Of course, if he is very tired and wants to go to bed earlier, then that would be fine. Once you start giving up naps and/or waking him up earlier, many kids will naturally get tired earlier and want to go to bed at an earlier bedtime.
Keep in mind that 'bedtime' here is defined as the time that your child actually falls asleep. If it takes 10-20 minutes before your child falls asleep once you start your bedtime routine, add that time to his 'bedtime' which will now be earlier.
How about older kids? For them, the problem isn't usually giving up nap time, but instead getting used to an earlier bedtime and earlier wakeup time.
A nine year old needs about 10 hours of sleep. If your child is used to staying up late during the summer and typically sleeps from 11pm to 9am, then getting up at 6 or 7am once school starts will be hard. To still get 10 hours of sleep, she will now have to go to bed at about 8 or 9pm.
High school age kids need about 9 (14 year olds) to 8 1/4 (17-18 year olds) hours of sleep a day. A late sleep phase is also important to fix at this age.
So that it doesn't make his first day of school any more difficult than it has to be, it is best to get your child on the sleep routine he will have once school starts as soon as possible and at least a few weeks before school starts. During this time, it is best to keep to as strict a routine as possible, with the same bedtime and wake up time each day, even on weekends.