The truth about the quality of Khan Academy's lessons/videos from this Washington Post article. The lesson for me in my 5 years of combing the internet for lessons and resources for middle school students is there has yet to be any site that does all the work or is a silver bullet for 'student ignorance'. - Especially one that just explains - ex=out and plain= to lay flat => which results in flat one dimensional learning. However, this site can be helpful as a resource for students to go to when they need more explanation on a concept or specific skill.
Read the article here.
Read the article here.