Depends on the country, but, generally speaking, it went from widespread to rare in one generation, and never was mandatory in the age of compulsory schooling.

Not sure what your point is - teaching of (non-classical) fiction in schools is itself very new, only a little more than a century old, and if you look at the mandatory fiction reading list in 1910s, 1930s, 1970s or 2010s, you'll see a lot of changes. So clearly teaching of literature in school doesn't stop Great Works from being reappraised.