School is mainly subsidized daycare, but it's daycare that's important especially for poor kids.
This is an important point in the United States. Many kids have absolutely NO order in their lives outside of school (due to absent parents, economic hardships, etc, etc). Many schools don't fully understand this, and do a pretty poor job of serving the kids, but I've seen public schools that fully understand what their kids need, and do their best to meet those needs. We can argue forever as to whether public schools should be responsible for the sort of things they are forced (by reality) to implement, but without the schools, these kids would be totally lost.