The content is great, and it’s free, so I don’t want to sound like a jerk, but... when it comes to the spelling exercises, it’s a nightmare. The previous page keeps popping up whenever I try to tap on the letters close to the edge. It took me almost 3 minutes to finish an exercise which is supposed to be 20 seconds. Also, when user is halfway through an exercise, switching to other apps (replying messages, looking up dictionary, etc) results in losing all progress of the current exercise. I believe it would be better if it could somehow retain the information in cache for a few minutes.