DS4 goes through cycles too. They can last for any amount of time depending on when he feels he learned enough for now. It can be frustrating to constantly hear about the obsession but I am also really enjoying the lesson.....:-) Right now it is ALL about geography. The slightly annoying thing about it is to constantly be quizzed and the fear of not getting the answer right. CAN be a bit irritating to get corrected by a 4 year old....