The above suggestion is good but i will take that a bit further.

But first of all, see your school guidance counsellor. It would be good for them to know but they can also be of help finding you options to challenge your intellect. One such example would be to set up the IB (International baccalaureate) program which you may be able to either 1) challenge for credit, or 2) sign up for.

If they are no help, look this up yourself and see if you can find courses online. Check to see if any universities in your region offer distance education. You may be able to earn university credit. If cost is an issue, most universities allow people to 'audit' classes free of charge. Another option is to contact MENSA, an association for the ultra gifted. They may be able to help you with some resources too. Finally, tutoring isn't just for the those with learning difficulties. Many tutoring agencies offer material and guidance for those who are not being challenged in a regular school setting.