How do I stop my child going out at night after school for so long on a school night?
Firstly, this is much easier when the ground rules are laid very early. For instance: if you have had an absolute rule with your child up to the age of 14 that school nights are only for family, extra curricular activities (sport, music, drama, etc), homework and relaxing at home then you will not have too much trouble continuing with those rules through senior high. On the other hand, if your child has had the freedom to enjoy other social activities on school nights in his or her pre-teens and early teens that will be a very difficult habit to break.
But if you are reading this question you are in the middle of dealing with this issue now$, so here are some ideas that might help regardless of your history.
The first step is to help your child see the point in coming home at a reasonable time. Most kids who lack personal discipline also lack a sense of purpose in their lives. Listen to what your teen wants to do with his or her life. Then when the issue of late nights arises use that ambition as the reason for the boundaries you are setting down.
Secondly, set clear, consistent rules. Perhaps allow certain days of the week for socialising (choose evenings before the school days that have the lightest academic load). Make the curfew one that allows some freedom but is not overly generous. 10:30 is the latest any teen should be out socialising on a night.
Thirdly, introduce consequences. These should be discussed with your teen beforehand and agreed with by him or her. The consequence should be real, but reasonable, and must be enforceable. Then enforce the consequence, never back down no matter how much abuse you receive. The consistent application of consequences is the best form of discipline (and control) available to parents today.
Fourthly, reward. Make it worth your teen’s while to be at home on school nights, studying. The reward might be extra time out on the weekends, or it might be the building of a bank account towards the purchase of something special. The actual type of reward is not important, the fact that it is guaranteed and centered on something worthwhile to your teen is.