Blue Spring Farm was an experiment in a sort of junior MacDowell work colony, run for young music students. The Shermans, half French -- Denis and Anne-Marie, resented having the summer imposed upon them; and the two boys from Illinois expected to get away without work and rejoiced in what they hoped would be an extra month of vacation. But things didn't turn out that way, and bit by bit the magic of Blue Spring Farm, the tiny experiment in international living, the inspiration of good teaching brought the four youngsters into line. The story is new in setting- there's much of value here. But unfortunately, there's an intangible aura of priggishness, of goody-goody atmosphere that spoils the natural spontaneity of incident. Overstress on music, for any but musically inclined young readers. And not Claire Bishop at her best.