What can parents do to improve the situation in American schools?

I've read a lot of rants from teachers over the past decade and observed reduced literacy on average in people only a couple years younger than me (class of 2015; I'm sure the decline was ongoing while I was in school, but it seems to have fallen off a cliff after I left, just anecdotally).

My son is 3 and starting preschool this coming fall. I'm concerned about readiness, inattention, and many other issues that teachers say are ubiquitous across students of all ages now, and curious what teachers think parents of all age groups can do to prime our kids for school to improve their experience and other kids' experiences, which I think necessarily hinge on teachers' capacity to teach. The new "normal" is clearly inhibiting that capacity, and it seems like many of these problems start at home.

What are the main things parents can do to help?

(I have a friend who's a teacher, and her stories have basically petrified me, lol. I am still clinging to the idea of public education for my son.)