Isn't the coefficient on 'T', the predicted 'mastery' variable, pointing the wrong way in the final logistic regression? And 'E', which is just getting 85% of the exercises right, is completely dominating all the other stuff (exponential moving average, etc) they did in the model.

So while all this is really cool, and I like the idea of doing EM on missing data (I've done it myself), it doesn't seem like it actually adds much, if I'm reading that right.