Shannon,

Due to budget cuts in education, summer school is often one of the first services to go.  Since I don't know the details about your son's difficulties, it is hard to answer your question.  However, here are a few ideas:

Check your town's local library.  Sometimes they offer special tutoring for children that are struggling.  You can also get him a library card so he can check out books on the subjects he is having trouble understanding as well as a few books he would like to read for fun.

Contact the local Boys and Girls Club.  They have programs that run all summer long and several of them offer tutoring.

Ask your religious leader.  If you belong to a church, temple, or other religious organization, they might know of a member who would be willing to help teach your son.

Private tutoring.  Chances are a teacher at your son's school would love a summer tutoring position.  This can be costly, but the one-on-one instruction by a trained educator can be priceless.  If you do decided to go this route, interview several teachers to find the best fit for your child.  Ask them for references and then call them.  Another thought along these lines to to hire a high school or college honor student who excels in the area your son is having trouble.  Once again, interview and call references.

Hope sone of these ideas work for you and your son.