To wonder when nursery and pre-school started being called "school"?

[RedskyThisNight]

As per title really. There seems to be an increasing number of threads where the OP talks about their DC going to "school" so responders naturally assume that the child is at "school" for 9-3 type hours, is at least age 4 and goes there every day. Only for the OP to reveal later that their DC is only 2/3 and actually goes to nursery/pre-school which quite often fundamentally changes the answers.

When and why did this change in terminology happen?

I follow an IG who calls it school often, since her ds was about 2.

The other day I had a huge shock when someone mentioned their youngest is starting school in March. Their youngest is 5 MONTHS OLD!!! It's a nursery attached to a pre-school. 'He will be 6 months old on his first day of school'. LOL