One reason educational material is poor is that it's inevitably written by someone who finds it hard to imagine what it's like not to understand it.

This is why all such material should come with commentaries by thoughtful students which explain it in different ways and link to additional resources. And with commentaries on the commentaries, etc. (We all have different misconceptions.)

There also needs to be a mechanism for rapidly correcting errors. Not every few years but every few days. (Text books are full of errors.)

All of which suggests that we need more educational material which is online, open source and wikified.