When I went to Sunday school, it was called CCD. At my parish, it is called Sunday Morning Religious Ed. (SMRE).
Probably your confusion is complicated by the fact that religious education as been very poor for the last 30 years or so. My parish has a decent program, however most of my students’ parents–my age or a little younger themselves seem to have little catechesis.
In my third grade class, I was not surprised that most of them didn’t know what the Trinity is. I was surprised that they didn’t know any Bible stories like Adam and Eve, Abraham, Moses, David and Goliath. None knew who the first pope was or who the current pope is. None knew that Judas was the apostle who betrayed Jesus. A handful don’t even go to Sunday Mass. They go to SMRE while their parents attend Mass.
But…this program is 100X better than the one I went through for grades 1-11. I was an attentive student but my knowledge was so poor I didn’t know any basic facts about Catholicism–not even the Real Presence. The only reason I knew Bble stories is that I enjoyed reading them on my own. It’s a miracle that I’m still Catholic. My sister and brothers aren’t.
So, even if your friends attended Sunday School, that doesn’t mean they were educated in the Faith. Even the best programs will have only a small impact if no formation is going on in the home. Consider, one hour a week for eight months of the year–taking out some weeks for holidays. It’s just not enough.
And, sadly, most Catholics so ill educated don’t really know that there are huge gaps in their catechism.
I started learning when a DRE handed me a catechism the week before I began teaching 7th grade CCD. Agh!!! I was so unqualified to teach any catechism. That poor class. Fortunately, I took time to read the Catechism which led to other reading.