I had my two oldest doing science together until this past year when one was 6th and the other 7th. My 7th grader did General while I did a different book with my 6th grader. I had been worried about the reading in General b/c it was definitely a step up from what we had been doing. If I could do it over, though, I would have them do it together and would purchase the audiobook to aid my 6th grader. In hindsight, he would have had no problem grasping the content, and then I could have kept them together. (At least a little longer!)