to think that the spread of ability is greater in EYFS than at GCSE?

[pickledsiblings]

Does anyone have any data on this or any anecdotal info?

Obviously it depends on individual cohorts.

I think that reception must be one of the toughest year groups to teach. By key stage 4 its fairly obvious who has problems and who is a genius. Ideally support has been put into place years before children approach GCSE.

Teens are pychologically more complex. They have completely different problems to a typical five year old. A five year old doesn't have teenage hormones.