SchoolChildren and Teens will have to go to school every day of the week, from Monday through Friday. This acts a lot like a Career, in that they have a job performance rating (their grades), which they have to be in a good mood before they leave to increase, and that they have some off-hours tasks they need to perform in order to do well in school (namely, their homework).
If you want your child or teen to do well in school, there are three things you need to focus on. The first is their Mood. If they're in a good Mood before they go to school, then chances are they'll gain a plus mark after their grade display. If they go in a bad mood, they'll often earn a minus mark.
Secondly is the aforementioned homework. Homework initially takes a long time to do, but if you ask for and receive help with homework from an adult, you'll eventually be able to do it twice as fast. When you have completed all your homework, you'll receive a one-letter increase in grade level after your next day of school.
Lastly, you'll have to ensure that you attend school every day. If you miss school, you'll lose a letter grade for every day that you're absent. If you fall all the way down to an F, you'll get fired from your job, if you have one. If your Sim gets an F two days in a row, she'll be removed from the lot by the dreaded Social Worker.
Getting into Private SchoolIn addition to the normal public schooling, you can also attempt to get into private school. There are a number of advantages to private schooling. For one, teenagers will be able to start a new part-time job at level two instead of level one. The hours are also slightly shorter for teens. You also don't have as much Need degredation from a day at private school if you compare it to a day at public school.
Of course, getting into private school isn't a matter of just applying; you have to have good grades (a C or better) and you have to invite the headmaster over and impress him. You can call him up on the telephone; he'll usually arrive at five PM on the same or the following day, depending on how late you call him.
When the headmaster arrives, you'll have up to six hours to impress him, by accumulating 100 points on his impression meter, or whatever you choose to call it. In order to do so, you'll need to serve him a meal (have the Sim with the best Cooking score do this), then give him a tour of the house. This tour will take you from room to room; when you reach a high-Environment area, click on the headmaster and select Show Room. You'll gain points in each room based on its Environment score.
Lastly, you'll have to schmooze with the headmaster. Any member of the household can attempt to do this by interacting with him; if you manage to build up a healthy Daily Relationship with him, you'll gain points here. This would be a good time to use something like The Eclectic Energizer; the better Mood your Sim is in, the more likely you are to successfully knock out a positive interaction. You can also gain bonus points by luring the headmaster into a hot tub, serving him coffee, or by getting him a drink from a bar.
If you manage to sufficiently impress the headmaster, he'll let you know that your kids have been accepted into his school. As of the next day, all of the kids in the house with C grades or better will begin attending private school. If you didn't succeed in impressing him, you can keep calling him back as often as you like until you succeed.