Squiggles, my T and I discussed this age a few times, especially how much the world changes for a child when they begin school. And probably it was more of a dramatic change for those like me who began school in the late 50's era.
From the cozy home we are suddenly spending most of our day in another place, a structured environment, with other children and adults that we don't know.
We have many responsibilities about being a part of a group, doing work when told to, etc.
Imagine what an adjustment that must be. A kid might feel like crawling up on the couch for some quiet time, but there they are at school instead.
Imagine how many parts of it could be scary. And that it could be lonely for shy kids.
So many things are part of the school years. It is one of the biggest transitions a person makes, and so big for just a little kid.