What is Progressive Education? Bred of the 20th Century, it is old enough to have been called by Harvard's late great President Charles William Eliot "the most significant movement in American education today." To carry it forward was founded, in 1919, the Progressive Education Association, which now has some 7,000 members. The philosophy of Humanist John Dewey and the work of pioneering Colonel Francis Wayland Parker (1831-1902) of Quincy, Mass. and Cook County, Ill. are implicit in much Progressive teaching. That education at any age should grow out of free individual experience rather than from books is a Progressive fundamental. Because parents who send their youngsters to Progressive schools are of necessity liberal-minded people, and because the system demands their active cooperation, it does not yet represent more than a strong minority in U. S. education. With some methods sharply defined, others vague. Progressive schools in general turn out children who are keenly observant, able to amuse themselves, often undisciplined in manners, adept at using their hands, sometimes foggy as to specific facts. Nearly all Progressive schools are in cities. Four of the best-known ones are in New York: Walden, founded 19 years ago by Margaret Naumburg, has a set daily program but endeavors to make the children self-reliant (from babyhood through high school age), permits them to call their teachers by first name. Lincoln School, experimental offspring of Teachers College at Columbia University, has received nearly $6,000,000 from the General Education Board (Rockefeller), has counted among its pupils Nelson and Lawrence, sons of John D. Rockefeller Jr. The flourishing Dalton School, just off Park Avenue, is famed for its course in live babies (TIME, Jan. 4) and the ''Dalton System" of its Founder Helen Parkhurst, a method of learning-by-doing which the U. S. S. R. adopted, but dropped this autumn because young Russians loafed at it. The downtown City & Country School (once the Play School) centers all its activities in work, teaches arithmetic, geography et al. in the school store and school post office, as well as by field trips throughout Manhattan. Fortnight ago came news of another Progressive school, young and bold, in many respects unique in the U. S. Croton-on-Hudson. N. Y. is a quiet village near Harmon, where New York Central trains exchange steam for electricity. The sprawling, bridge-playing, gin-drinking suburbs of New York have not yet entangled it. In Croton, seven years ago, settled Economist Stuart Chase, his wife Margaret Hatfield, Elizabeth Moos, a former teacher at Walden and other modern schools, and her husband Robert Imandt, violinist, onetime French Army man, camp director. Between them Miss Hatfield and Miss Moos had three children. They wanted to teach them. They went to it in a garage. Soon other families sent their children over. When the number grew to 16, Teachers Hatfield and Moos realized they had a School At the beginning of their third year there were 29 pupils, five teachers, installed in an old farmhouse they had managed to buy. From the surrounding country, where George Washington skirmished with King George Ill's mercenaries, they took the school's name: Hessian Hills. More & more people heard of it. Since its founding, 30 families have moved to Croton to put their children in Hessian Hills. Some of the parents: