It was a long time ago but from what I remember
1. All our kids went to Preschool. I think they were hard to cope with when 2yrs - at that age they are into opening every cupboard and drawer ... basically on the move all the time and driving everyone nuts - and it did not seem fair to unleash them on someone else. They would have started Playcentre going on to 3yrs.
2. They all went to the local public Primary school. By age 4yrs kids start to get 'stir crazy' and they start to drive mothers crazy - school is the only solution, but schools are very sensible in that they do not want to be the ones driven crazy and delay entry.
All the kids went to the local public Primary school and everyone of them enjoyed the experience.
The school had a starting scheme whereby, at age 4.5yrs, the kids could be brought in on Wednesday afternoons. It was a good way to introduce them, in a managed way, to the life and routines of school life.
By the time they turned 5yrs they were able, and eager, to start school full time.
A long time ago I was visiting Brisbane (Australia) and I can remember a mother telling me that in her area girls started primary school on turning 5yrs - but as boys had not attained the same degree of 'socialisation' their entry was delayed until age 6. She said it really worked.
The best thing about school is that it tires kids out so much that they become almost manageable.