Thank you. I take your point. Where they are interchangeable (probably a better word in this context) is 'are going' or 'go' . So we go [shopping | to the shops] or we are going [shopping | to the shops] etc. But I do understand that direct translation between languages is not easy and Polish in this instance may work differently. As always thank you so much for all your work and replies.
Well, you "go to the shop every Sunday", but you "are going to the shop right now", don't you? And while 99% of Polish verbs don't show this difference, Verbs of Motion do. If this sentence was about any other destination than school, I wouldn't accept "go".
I wrote that it's among the accepted answers for "idą" for some reason, maybe I was in a hurry... not true, it's just accepted for "idą do szkoły". I don't exactly understand why, I've been explained this a long time ago and I just accepted that it works, but I'm not sure why. I believe it has to do with some more idiomatic usage.