No it's not my daughter, and nobody's cross about it. The parent wants to understand it all better. Without knowing more, their concern is that the child might not in this particular middle set cover as much ground as they are capable of. I am only used to grouping children by ability at secondary level, or deciding on lower tier / higher tier GCSE papers. Even then it's scary to think that you might have limited the opportunities of an able but underachieving child by putting them in a lower set. Fixed groups by ability in early primary sound scary to me. It's different for you experts in the field as you know how it all ticks.