This Supreme Court Case began when
McCollum, a mother who happened to also be an atheist, was infuriated that her son’s public school taught him a religious perspective. Her son chose not to attend the classes, then was ostracized by the board of education. McCollum sued the board of education on July 1945. McCollum won the case, and the school stopped teaching the religious classes.
The answer to your question would be due to religious teaching in the school system, or something along those lines.
I hope this helps <3