Look over your school transcript and consider the following two questions: Do you have enough units to graduate on time without summer school? Are there electives that you want to take but can't fit into your school-year schedule?
Consider summer school if you answered "yes" to either of these questions, especially the first one.
Think about other reasons to go to summer school: to take a certain class from someone who doesn't teach it during the school year, to brush up on a rusty subject, or just to keep your brain active over the summer months.
Balance these factors against the downside of summer school: spending money instead of earning it, missing out on summer fun, not getting a break from the school-year grind.
Consult with your academic counselor, explaining the factors you've been weighing. He or she will be able to offer you additional advice.
Choose a program that's right for you, if you decide to go (see Related eHows).