EDIT: and my school district was staggered the wrong direction. High school started earliest, then middle school, then primary school was latest. That's backwards from how it should have been, if anyone in my city had understood how the circadian rhythm changes during adolescence.
I had trouble adapting to an adult sleep schedule from a very early age, and had some embarrassing episodes, as well as weird stuff like slipping into a dry bathtub late at night because I wanted to read a book.
In high school, I began checking out, and my depression was chronic and major. I had a "girlfriend" (who was abusing me) so I stayed up late at night on the phone or visiting her. I was falling asleep and falling behind in classes. My parents were beside themselves. It didn't get any better.
I've literally been fired from jobs where I was one of the better performers for the singular reason for struggling to be there at 8am every day, and where this didn't matter at all for the position if I started at 8am or 10am (for some positions it obviously does matter). That I often worked longer than many others didn't seem to matter; people take it as a marker and that's that.
5:30am is utterly ridiculous; that's just the middle of the night.
There's actually a time that's generally closest to the middle of the night as measured by the start and end of the night. In fact, it's shortened from that very phrase "middle of the night". It's called midnight.
In summer around here, 5:30am is approximately the end of the night, as measured by the sun.
The explanation I always heard for this structure, very common in the US, is to allow for after school jobs for high schoolers.