I am a little confused by the term "maturity level" and my answer is going to be based on what I think perhaps was assessed -- academic developmental level. There are many ways to help a child make up some basic skills. Ask the school to test him for learning disabilities. After the testing, the school will meet with you and devise an educational plan; this may include resource room, where he will get help in his subjects and in study skills. If he doesn't qualify for resource room, work with his school counselor to get him into those classes and with those teachers who can best meet his needs.

Enrich his learning at home with books (everybody in the family should read at the same time), travel, outings, academic camps, building projects -- any kind of activity where he can use numbers, map-reading skills, etc. There are usually learning centers in larger cities that are a great place for remediating basic skills.

This is not an overnight solution, but by constantly involving your son in the excitement of learning, especially in everyday real experiences, he will learn those things he needs to know to be self-sufficient and happy.