THE FAMILIAR pattern of the academic year -- nine months of classes, three of summer vacation -- got started because most children needed June, July and August at home to work in the fields. By now the cycle is so deeply ingrained that just about everybody, in school or out, thinks of the year as starting in some sense after Labor Day. It's so ingrained that when the school board of Los Angeles County recently voted to begin moving all its 600 schools toward a "year-round" school schedule instead -- with several shorter vacations and different "tracks" of students rotating in and out of classrooms -- parents in affluent areas tore their hair and warned of massive pullout from the school system. They said the staggered schedule will play havoc with day care, family unity and vacation plans. But officials who have experienced the same shift in other districts were largely unimpressed. If their experience is any guide, they say, the disgruntled parents -- and many more besides -- will soon be returning in enthusiastic droves.

What's so great about year-round education? A lot of things, it turns out. Most schools that have tried it -- there are about 400 so far nationwide, including, briefly, Prince William County -- were driven to the expedient by overcrowding. Some schools give two six-week vacations, others as many as four three-week breaks per year. Such "multi-track" scheduling saves money by making room for more students and using facilities more fully. But aside from economic considerations, year-round scheduling turns out to offer educational benefits. A prime obstacle to teaching nowadays is the huge amount that students forget over a three-month summer. The students who forget the most are the ones from disadvantaged homes or homes where no English is spoken, so the gaps in achievement between rich and poor get wider every autumn. School districts that offer both systems, year-round and traditional, say the differences in academic achievement become apparent in as little as two years.

A small group of reformers, citing these benefits, has been touting year-round education since the late '60s, and a handful of schools across the country operate year-round even without overcrowding as a spur. In general, though, the status quo has a profound hold on people's biorhythms and social patterns. Changing over, say those who have done it, requires slow, patient persuasion and lots of options for outraged parents. (The L.A. plan lacks these, and may yet fail in a second vote this spring.) On the other hand, the economic logic of year-round scheduling is a powerful incentive, and the general atmosphere of education reform enthusiasm has made people more receptive even to ideas that might otherwise have struck them as fringe. If the Los Angeles schools can make a go of this one, they will be well worth watching.