In an ideal world children who were 10 years old and couldn't read would have one to one tutition. It must be horrible for a 10 year old to be put with a bunch of five year olds. The problem at Monteagle is that there are so many non readers.
Prehaps they could have grouped all the older non readers together, but it would have created a sink set and discipline would have been a nightmare. Prehaps by mixing the older children with the younger children they were hoping to get an easier to manage class.
I think that mixing children across years is a good idea, provided that the age group is not too extreme. An august born child might be at a similar level to a September born child. I thought it would good that the little girl who had learnt to read before starting school was able to be in a group at the right level for her.