I wanted to have my DD in a 1/2 class when she entered first grade becasue I felt she was ready for it and it would be good for her. The principal disagreed and she was in a regular first grade, then a regular second grade, and did very well academically and socially. Ironically, this same principal assigned her to a My daughter was put in a 2/3 class of about 20 children for third grade, despite my request that she be put in any of of 3 other grade 3 only classes. I expressed reservations to both the teacher and the principal, very specifically, knowing my own DD better than they did

My concerns were that because she was bright and a quick learner, at the end of the year she would not be at the same place as far as proficiency in the math and reading/writing skills as she would be if she were in a regular third grade class. The teacher was quite snippy about that and stated that the objective wasn't to "get her prepared for 4th grade", it was to see how far she could get with the third grade work....and despite my trying to explain my concerns she assurred me that my DD would do just fine. I was also concerned because DD was by nature outgoing and somewhat of a social butterfly...OK, maybe a busybody

and I feared that if she finished her work papers and so forth and had time left over, she would be "helping" or bossing the younger kids or just being social when I would prefer she be challenged with her schoolwork. The principal assurred me that this would be a great year for DD and that the teacher knew how to teach the multi-age class, and he really neded to do this for the "balance" of all the 3rd grade classes. Well, I decided not to make waves and to "go along" despite my reservations. DD was reprimanded on a few occasions for talking too much, but we could live with that and it never got out of hand. But my fears on the academic side were justifiable...although she got good marks all year, her class did not begin multiplication tables at all as the three other "grade 3" classes in her school did. So fourth grade math was a struggle for the first month until I sat down with that teacher and we went over what the problem was, worked up an "at home" plan of attack (flash cards mostly!) to get her caught up to speed, and by the end of the year she got an award for math performance much to her own and our delight. Unfortunately the whole experience planted an "I'm not good in math" seed in her head and it has taken considerable time to erase that preconception from her.....her 8th and 9th grade math teachers helped a lot and she just ended her sophomore year in high school with a 90 in Advanced Algebra the 4th quarter, to round out a "high honors performance" Anyway, don't mean to turn this into a brag about DD, sorry
I think you have to think about your own child's personality and development, and get a feel for the teacher and school philosophy. If the teachers are well-trained and embrace the whole concept and the classes are not large so that each child CAN be challenged to their level of capability, it would be OK. Unfortunately our experience was not positive. As you can see...it's still pretty vivid in my miond even though it was over 7 years ago!