I would like to suggest that students have more than one try per problem on practices and quizzes. I find that my students often become very frustrated when they miss a problem due to a silly mistake. I know students can retake practices, quizzes, and tests but fixing a simple mistake is not worth doing the entire quiz or practice again. If they could fix their answer, my students would get less frustrated and be more likely to succeed on Khan. It's important that students can look at their OWN work and try to figure out what they did wrong before they jump to the solution provided for them.