School is a huge part of most people's early lives, to think you can replicate all of the cultural and social experiences that take place there wholly in extra-curricular activities, i think, is misguided.

I like Salman Khan's approach, which put simply is this:

Learning takes place at home, students can go over material at their own pace.

'homework' is done at school, where children are able to ask questions about the material, helping and receiving help from other students and teachers.

This may be similar to a 'home school co-op' as you mentioned, but i dont know.