My previous sentence sets the principle, your answer rejects the principle on an all-or-nothing basis, my following comment clarifies the application of said principle within the comparatively narrow setting of schools.

I’m not sure what’s left unclear.

It’s not about preventing religious conflicts. It’s about not giving those conflicts a forum at school, the place where children learn to be tolerant from people who aren’t their potentially fundamentally religious parents.

The problem isn’t any spiritual or religious connection the children form. The problem is that most monotheistic religions are very rigid in their exclusive prerogative of interpretation concerning all things fundamental and truth-related.

Having more than one exclusively-dominant religion represented in any one space must lead to unsolvable conflict. Contradicting absolutes cannot tolerate each other.

Given that a functioning state must necessarily assume the role of a sovereign, banning religion from public spaces is pretty much the only solution for preventing religious conflicts.