My brother is doing 'summer school' right now. (It's actually a class at the local community college that lasts for four hours every Tuesday and Thursday night.) He's doing it so he can get three years of languages for his credits and go to a decent college/graduate highschool. (At our highschool, you have to have three years of languages.) When you get there, see if there's anyone you know! Even if you're not great friends with them, you guys could still hang out with each other and become better friends (my brother met some completely random girl, who he didnt' even know he knew (she was my big buddy in elementary school, she's my best friend's older sister's friend, and she's my brother's friend's cousin.) and now they're carpooling with each other and have actually become friends.
Make sure you pay attention in your class, and do the best you can. Remember, you have to take a whole year's worth of math and cram it into one summer! That means you have to pay lots of attention, and make sure to do your homework.