Improving grades matter. This means your presumably junior student can have better grades his spring of junior year semester to show he can do the work for the colleges interested in. Of course the students who caught on early will have better chances. His Hs likely will prepare him for the rigors of college work more than the average HS.
Do NOT try to game the system. It could backfire in many ways. Needing to adjust to a new system will be stressful and there are no guarantees he will do any better.