This kid is very very lucky. Obviously they violated the CFAA which carries severe criminal penalties. They engaged in actual hacking without any permission or defined scope. And they exploited the system without any responsible disclosure process.
Anyone in the field will tell you that this is an absolute disaster of a post because it sends the signal to other young aspiring cybersecurity professionals that this is OK, and the school will laugh it off, and you'll be seen as an adorable Matthew Broderick type Wargames character. I can't overemphasize how far this is from the truth in 2021.
Absolutely do not access systems you are not allowed to. If you do want to do penetration testing, you need permission from the systems owner and a clearly defined scope. And when you do find issues, you don't exploit them, you responsibly disclose them within a clearly defined framework.
If you want to end up with a criminal record that will profoundly effect the rest of your life, including your career prospects and ability to travel internationally, then by all means, do what this guy did.
I wish it wasn't so. It never used to be. But this is how it is now. Overzealous prosecutors have been given a huge amount of power, and all you need is one embarrassed systems administrator, school board or management team to trigger a disastrous outcome in stories like this.
At the school my child attends, I am confident he would have ended up with a pat on the back if the circumstances were similar. I can't speak for the district -- I'd be willing to bet that'd be very risky. At the school I had once attended, I'd expect the entire district would behave similarly. I'm sure there were people within the district administration that wanted to throw the book at the kids involved.
Here's the thing for those people: the last thing a school district wants is to become national news for punishing a bunch of kids who the evening news can make out to look like "Geniuses". Since nothing failed in their plan -- that's crazy important -- there would be very few ways to frame the story that makes the administration look like anything but bullies, and many will frame them as "petty bullies". I have a friend I went to High School with who is now a High School principal. He's still "that guy I went to High School with." I have no doubt he would have given the kids an award privately, if not publicly.
It's sad that some public school districts are using discipline approaches you'd expect to see in prisons, rather than a school, and I'm sure in certain places in the country, that might be a necessity. Context matters, too -- were these kids who were constantly pulling pranks like this, had been talked to in the past/impacted things in the past, etc, I'd expect a harsh response: "Yes, we get it, you're smart, stop breaking things already, read the horrors of the 1986 CFAA because that's coming if it happens again." I'm guessing these were otherwise good students.