You have to wait 20 years for the returns to society. Public education was enormously successful when it was introduced in the 19th century. There's just no profit in waiting for second order effects to kick in.
Diminishing returns. Per-student education spending has been going up since 1990 except a dip during the 2008 recession. Adjusting for inflations it’s now double what it was 30 years ago.
So was Rural Free Delivery. Farmers being able to communicate was a massive boon. There is a channel for farmers called RFD tv. They completely scrubbed the free provided by the government part after private equity bought the tv channel targeting farmers. Then they got Imus in the Morning so farmers listed to Imus, Rush, Hannity, and orielly forgetting the government helps them.