From Joanne Jacobs … Critics hit the math of Khan:
A ”Mystery Teacher Theatre 2000″ video by two Michigan professors, David Coffey and John Golden, pokes fun at a Khan lesson on how to multiply and divide negative number. (Sal Khan responded by posting a revised lesson.) Dan Meyer, a Stanford University doctoral candidate in education, who blogs at dy/dan and Justin Reich, who blogs at EdTech Researcher, are offering $750 in prizes for the best online critique of Khan Academy videos. The deadline is Wednesday.