School might be a mechanism, but I doubt that's the driving force. Losing a sense of curiosity and play is an ancient phenomenon that predates modern education. When I became a man, I put away childish things was written 10^3 years ago.
If schools are doing X, Y, and Z and students are losing curiosity, stopping X Y and Z might not do any good unless it's part of a broader cultural problem. More importantly, the question of whether schools are the best place to prod cultural forces remains open. If we do decide to curate curiosity in schools, it might be beneficial to understand why curiosity is dying in the first place.
I'm curious if anyone has any insight into what these forces might be and why they're so universal. Unless losing your sense of wonder is a relatively recent transformation, why did humans evolve in such a way that wonder isn't conserved across development?