Sorry Sink, its been 5 years since I reviewed this stuff.
Rome didn't exactly say it was a mortal sin to send children to public schools, they only said that if parents persisted in doing so they cannot receive absolution in the Sacrament of Penance, which infers it is indeed a sin, one grave enough to have to specifically confess.
But you're probably right, these old documents make them Popes look foolish. We all know the problems with public schools of a century ago have pretty much vanished, and that government schools, since the so closely obey all the things outlined above, are no longer a danger to our kids, and their Catholic faith will always be reinforced, enriched and nourished within the hallowed halls of governmental academia.
But, they can receive absolution, since they do, and have for as long as I've been alive, even in pre-Vatican II days. Catholics don't confess that they send their children to public school, since there is absolutely no sin involved.
It is not a sin, of any kind, to send children to public schools. That is absurd on its face, Brian.