In terms of extra curricular clubs:
A club for Year 7 students may involve students from different year groups helping out. For example if it was sport-related, then Year 8 - 10 sports leaders may be involved. If it was computer science related then Digital Leaders in Years 8 - 10 may be involved. Without the assistance of the older students, the teacher may not be able to run the activity. Also the younger students don't get to meet students in other years who share their interests. The older students don't get to develop their leadership skills.
Then there's the impact on Year 6 students. The activities that are part of their transition from primary to secondary were all cancelled when schools closed and have not resumed. Loads of older students were looking forward to helping those students when they get to Year 7, showing them round the school, helping them etc.
Parents of children who are among only a handful from their primary school are very keen for their children to get to meet other children in a similar position, and understandably so, and students already at secondary school who went to the same primary are keen to help, but yet none of that can happen. This is causing some children, and their parents, to be extremely stressed and worried.
Staggered break and lunch
times could be achieved if you recruit sufficient midday staff to work in schools, in theory. It would cost a lot of money and cause all sorts of other problems.
But lesson changeovers seem impossible to me. You cannot have different lesson changeover times for different year groups, so if the changeover time is the same, then students are going to be mixing in the corridors. How can they get around that? I can't think of any practicable way, so it falls down at the most basic of hurdles.
It's difficult for me to contain my anger at the fact that some people think this is actually a good idea. I'd like to have an argument with those people! That's the full argument, not the 5 minute argument