Different high school=different preparedness for college

A perfect grade at you respective school may not be an A at another school?? This is all news to me. In the article by Katy Murphy, she talks about how high school students, although academically at bar for high school standards, "about 20% of the freshman who enter Cal State East Bay with a 4.0 GPA need at least some remediation in Math, English or both...". Mike Kirst goes on to talk about students in their first few years of college:

In America, high school course content and homework demand and pacing is detached from college. If you’re not in AP classes, it’s really quite dangerous… It’s more common than uncommon” that students feel they are prepared from their college future in high school, but realize that they were wrong.

Worell also goes to comment about how freshman and sophomore students are seeing college:

Worell has spent years working with low-income, minority students and studying
the psychology behind their college experiences. He said they often arrive on
campus and discover they have a year or two of remedial course work ahead of
them. It’s common for them to feel they don’t belong, he said, and to drop out.

How I'm interpreting this article is that now its not only what colleges we go to that will help our future, but now we have to start worrying about what high schools students are going to? because they weren't as prepared because they went to a lower rated school, "where the standards are lower"? That doesn't seem right. I thought there was a law or something that made it so that all should get equal education no matter where from or what race you are.