Clearly that school sucks ass. Advancing kids without proper credit to hide just how much they're sucking ass. But mom is delusional lol.
Aware of it or not, your kid is late or absent half the time, that's on you. You know his grades are shit, you must have heard something or had an inkling that the school sucks ass, so you thought he was getting a pass since they were failing to leave him back. That's on you.
Yes, this could happen to anybody since probably most parents (at least in the US) are this clueless and reliant on the schools. But don't be surprised when reality hits. Admit your role in this failure. The school absolutely failed him, but so did you. It's your kid, it's ultimately your responsibility to see him through.