Children learn basic math and reading skills in the first three grades. Not as much time is spent on building these skills in the fourth-grade classroom as students begin to spend considerable time in the content areas, especially social studies and science. Therefore, repeating fourth grade is not likely to help your son improve his basic skills.
First and foremost, you must find out why your son keeps struggling in school. Schedule a meeting with his teacher, school counselor, and the individual(s) who tested him for learning disabilities. Before the meeting, ask that everyone come to the meeting prepared to discuss why you son is continuing to struggle in school and what can be done to turn things around for him. The school needs to present you with a solid plan on how your son can be helped. It is not enough to say that retention is the solution. Ask also about how you personally can help your child with his academics.
Please be aware that there are alternatives to retention. Summer vacation is rapidly approaching. This time should be used to resolve some of your son's learning problems. He needs individualized instruction from a tutor or learning center. Depending on the progress that he makes, you can evaluate whether or not repeating fourth grade would be beneficial to your son.