The drag and drop feature is amazing! Could you add an "immediate feedback" button to it? I is a behavioral option which I saw in the fill in the blank feature which says, "Automatically Check Answers After Input."
I am teaching my students how to solve equations with it (which is great!). I would like them to be able to drag a number or variable into the spot I have on the worksheet and immediately know whether they got that step of solving the equation correct or incorrect, before moving to the next step.