I notice you are in England, so I'm not very familiar with how your schools are set up. I can only tell you what would be available in the US. Maybe England has similar programs.

In the US, school districts must provide for education for the gifted and talented. In my district, I believe the initial recommendations for testing occur in 2nd grade. How the programs are set up varies from district to district, but basically students who qualify for GT are pulled out into a separate classroom at some point during the day to work with a teacher trained to teach GT kids. Often they are served through language arts classes and math classes, but that varies. You might check with your school to see what kind of testing programming are available.