My kids have had them many times. My dd7 is in her 2nd year in a 1/2 class. My son had this teacher, too, so I know it will be great. As a 1st grader she looked up to the 2nd graders and now as a 2nd graders looking forward to being the good example. It didn't work so well when my son was in a 4/5 split. There weren't enough 4th graders (5 vs. 20), and the teacher left them on their own to learn and figure things out too much. It was such a disaster that the parents had to band together and meet with the administration!
