As a kid, it's very easy to make friends. You don't need school for that. Three of my child hood best friends were not in my schools. I sill visit one regularly, 20 years later.
In fact, I'll argue that school distort the child ability to socialize, not improve it. Because it's an artificial setup were the crazy values and rules only exist and make sense in the school. And worst, adults sell you values and rules from the real world while you are stuck in this alternate dimension.
And it's an arbitrary cohort of same-age kids. Whereas for example my friends in the neighborhood all were of different ages. Not very different, but still.
That's the biggest thing schools do wrong, in my opinion. Children learn best from each other, but that requires mixing age groups so there's something for them to teach.
In fact, I'll argue that school distort the child ability to socialize, not improve it. Because it's an artificial setup were the crazy values and rules only exist and make sense in the school. And worst, adults sell you values and rules from the real world while you are stuck in this alternate dimension.