U.S. college tuition is growing at the slowest pace in decades, following a nearly 400% rise over the past three decades that fueled middle class anxieties and a surge in student debt.

Tuition at college and graduate school—after scholarships and grants are factored in—rose 1.9% in the year through June, broadly in line with overall inflation, Labor Department figures show. By contrast from 1990 through last year, tuition grew an average 6% a year, more than double the rate of inflation. In that time, the average annual cost...