It's relevant because the legal constructs we derive are not as absolutist as we would imagine and, that our society, particularly our education, was never entirely secular even long after such clauses were established, and large swaths of people have no understanding of that history, or the degree to which 'The Church' etc. fundamentally underpin these institutions.
Christmas/Easter holidays, 'In God We Trust' on every dollar bill, 'National Prayer Breakfast', Army Chaplains, modern/recent US Presidents (aka Jimmy Carter) teaching Sunday School in the White House etc.. 'Separation of Church and State' is almost an academic construct in a nation or culture in which faith (or even just religion) plays a major roles in people's lives.
Specifically with respect to education, I think many people think of 'University' as a fundamentally secular institution, when really it's not.
Frankly, the general orientation of 'Let's not have a religious state, and our institutions should not be religious' is a really good idea, however, it turns into a hairy mess at the margins.
In Ontario, Canada, about 40% of the 'Public Schools' (aka fully publicly funded) are actually Catholic. They are 'open to anyone' and it's not 'Jesus Songs All Day' kind of thing, rather, they have 'Christmas Concert' where they are allowed to sing Christmas Carols, whereas the regular Public Schools have 'Seasonal Concerts' with 'Wintertime Songs' as an example of some of the 'notable differences', by that I mean, the 'Catholic Schools' are not hugely religiously infused.
I bring this up because it's one of the oddest and most paradoxical arrangements in modern secular governance with respect to education. It's only controversial in the academic sense, i.e. something for people to argue about, in practice, it's the most 'normal' thing one could imagine. If one were to suggest this arrangement for a US state, all hell would break loose. Pun intended. Of course, the US is a different place than Canada. (FYI I'm not Catholic).