As I said, there really are no rules. Everyone just knows what is expected and that the priority is studying and homework and sports commitments. They prioritise their school related work. I don't stop anyone from going out with friends as long as I know where they are, and who they are with and what sort of plans they have for getting home. Overdoing the socialising has consequences that are difficult to deny -- they could lie about how they spend their time, but the school issues progress reports every few weeks. I don't have to hover or police. As long as they manage their time well and stay out of trouble their grades will stay up.
They have fun on weekends, and they are involved in school sports teams too, which takes up a good deal of time on weekdays and evenings and also on weekends from time to time. All of them had Saturday jobs from 16 on and all of them babysat at least twice a week year round from age 12. DD1 swam and played water polo and also did badminton. DS played football and wrestled. DD2 and DD3 did badminton. DD4 will probably play volleyball as she is tall and loves it. All of that involves early morning and after-school practices, and games or meets in the evenings on weeknights, with homework and studying squeezed in too. You have to have a C average to stay on the active roster.
By way of context -- we are in a mainly UMC suburb of a major city in the US where you can't party or even socialise too much the whole school year and then pull a few all nighters and get an A for a course in the final exam in May. You could certainly party hearty every night of the week if getting into a decent university wasn't your goal, and parties tend to be very 60s stylee, thanks to the affluence and the existence of two Catholic high schools within a two mile radius of where we live. There are a lot of teens who will get a car at 16 and a sinecure from Daddy at 18. OTOH, there is also a sizeable minority not interested in university who come from the wrong side of the tracks, and they are partyers too. We are right beside one of the most crime ridden areas of the neighbouring major city and there is some spillover in the form of drug sales, and prostitution near the train stations. There are a lot of tragedies involving ODing, unplanned pregnancy, drunk driving, and addictions, as well as smaller scale but still poignant wastes of potential. I have learned not to make any assumptions about any teen's character based on where they live or what their parents do for a living.
Along with the partying groups there are the nerds, goths, misunderstood poets, boys who build unicycles and ride them around, chess kids, music kids, artists, geeks of various kinds, home schooled kids, etc. My DCs fit into this miscellaneous group. By the time they are 14 most teens know who they are and what group they belong in. Everyone rubs along together pretty well in the high school, with a student population of 3600 that comes from half a dozen feeder schools. Monthly arrests of students for possession or distribution of narcotics are predictable. There is a large creche for the babies and toddlers of students. A large group heads off to Ivy League schools every year and another large group heads off to the local community college.
The DCs all know how the GPA system works. From age 12 onwards in school they were made very aware of the importance of consistent effort. Every piece of homework you turn in all year and every weekly test counts towards the GPA, on which your chances of getting into a good university depend. Your final exam might count for as little as 10% of your final grade for the semester. Having seen the makeup of the student body in the university DD1 went to, they all know they are in competition with hundreds of thousands of students from places like Shanghai and Singapore as well as American students for places in university.
I'm not Amy Chua but I could probably pass for her third cousin once removed. 