It was for like 2 hours one day/week.

There's a wikipedia page on the issue:
https://en.wikipedia.org/wiki/Released_time

I even think a bus drove us there. This was on Long Island in the 60s.

eta I knew Catechism didn't look right when I first spelled it

We had "religious instruction" during school as well once a week where students were released to attend (and very few of us were left behind, no pun attended). This was a public school.

Released time kids went off campus to their churches and got religious instruction for an hour, once a week.

Those of us, like me, who didn't opt into the program, stayed in their classroom. When I was in the sixth grade, my teacher taught the kids who stayed in class conversational Spanish. We didn't lose anything, but gained an extra bit of education.

Mostly in jr. high (sort of like Middle school) . Every morning, no pledge to the flag, no morning announcements, but out came the teacher's Bible and a student stood up and read a passage . Hated it with a passion.

(1985-1991) the Catholic kids left class half an hour early once a week to attend CCD classes (about a 5 block walk from the school). I'm not sure why the church didn't just push back their time to coordinate with the school schedule.

I remember being jealous they got to leave early until they informed me CCD stood for "Children's City Dump."