My 2nd son has been starting this blog/forum: https://highschoolstudyhel.wixsite.com/amasite to help high school students. 

This website will help you revising/studying by answering your questions. Currently, this site can answer questions about IGCSE Mathematics, Co-ordinated science, Economics, Global Perspectives, DT (RM), AP US History, Chemistry, Biology, Macroeconomics. If you have any questions, just take a photo of your question, and post in on the forum page.

Good start!