I have had two different children in combo classes, 2 years each. Like syoblrig, the problem we had was when my DD was in a 3/4 combo as a 3rd grader with only 6 third graders & 20 4th graders. This was especially a problem because there was only one other 3rd grade girl who was not an academic fit with the other 5. This was a disaster from the beginning, but it was more because it was a combo that was formed quickly, 6 weeks into the school year, with an inexperienced teacher, and without a lot of support from the administration.
One of the other combos we experienced was a K/1 combo with a 1st grader. Only 6 kindergarteners, but they were older and academically advanced. It was not a problem for my 1st grader.
The other two combos (2/3 as a 2nd grader, 4/5 as a 4th grader) were overall great experiences. The classes were evenly divided, hand picked, and with teachers willing to buck the system & differentiate by grouping my younger DDs with the older grade for reading and math. The years in these combos were great, however the real issues came the following years. The differentiation was not continued in the next class & there were many issues with boredom, tuning out, etc. With my DD who had been in combos for two years in a row, it was a real issue when the older class went to middle school & she was left behind - almost felt like she had been retained.
Some other issues that I am aware of with combo classes come with class field trips - especially when there are traditional field trips in the school for each grade level. This divides the class and takes the teachers away from children who cannot go on the field trip because they are in the other grade.
Good luck! Hope your DD has a great year.
