When I was growing up in
Toronto and
Ottawa, this was the term used for schools, still tenuously connected to the public system, but were different,
alternative in all other ways.
Sometimes called free schools they were modelled after the innovations of A. S. Neill, the English educator who wrote Freedon, Not License, and Summerhill.
These schools experimented with different discipline and attendance codes, dress codes, decision-making, and of course, curriculum. The central idea was that children learn at their own rate, when motivated, and that motivation is stifled in the large, indifferent public system.
In Toronto they went by colorful names, like SEED, School of Experience, Exploration, and Discovery, Knowplace, Superschool, Subway Academy.
I always felt that Lick-Wilmerding High School was one. Funny, I had to go to San Francisco to attend such a school. In Canada, I was stuck with the usual, boring, mind-killing sort of thing.
I don't think many of these schools exist anymore.
I have discovered that now alternative has become a euphonism for what previously was called special.