A major, major reason why classes are not the best option for ACT or SAT test prep.

I've often said that classroom instruction is not only sub-optimal, but also outdated. Classes just do not allow students to learn as well as they should. Obviously, when you're trying to learn in a large group of other students, you can't focus on only the issues you have trouble with and, even worse, you have to move at the pace the class moves, regardless of whether you understand the material. This TED talk by Salman Khan, the founder of Khan Academy, shows just how devastating this problem can be. 

At 13:50, Khan discusses the relevant part. He found that when students were allowed to learn at their own pace, there would be a group of kids who raced ahead and a group that was slower. In a traditional model, they'd be called "gifted" and "slow". But if you allowed them to learn at their own pace, the "slow" kids ended up racing ahead. Imagine that. Kids take different amounts of time to learn material, but that in the end, the slower kids could become gifted students if only allowed more time to learn the materials. How many students have lost that potential because they were stuck in a classroom teaching system that left them behind from the beginning. Private, one-on-one instruction: focus on only your needs, AT THE PACE THAT WORKS FOR YOU.