It wasn’t even anything groundbreaking… just a mandatory education till 18 years, although that could include trade learning, practices, internship etc. It was illegal and punishable by fines and state supervision to not send your kids to the school. This got retained even in the capitalism in every state afaik (there are holes now though since liberals defund education and the system is slowly rotting).

And yet, such simple policy is still apparently unthinkable for the capitalist countries, even rich ones.