You don't really have a choice in the middle school years... You read their text book and teach them. When they hit high school I'm afraid courses like trig, calculus, physics, etc. are a bit too deep to catch up on with an occassional read of their text book. Your role will be to hook them up with an upper-classman or college age tutor. In a highly competitive environment you'll find lots of kids with tutors - not to play catch-up, but to stay-up and get ahead.