If the school has not already suggested it, you should ask that testing for learning disabilities be done as soon as possible. No parent ever wants his or her child "labeled," but determining if there are learning disabilities present is the first step to getting him the help that he needs.
Teachers of exceptional children are trained in methods of teaching that can help children with learning problems, plus they have access to additional resources and materials that could help your son.
Neither you nor the school wants your son to repeat another grade. The research on school retention says that retaining a child does not help over the long run and may set the child up for problems later on. If a child is going to be retained, however, kindergarten or first grade is the time to do it.