THEODORE Sizer's fundamental principle of educational reform is "less is more." Schools can't do everything and must not try, for in trying to do too much, they often fail at their primary purpose, which is "helping adolescents learn to use their minds." The Coalition of Essential Schools under Sizer's direction has very specific directions for how that can be done.

First, classes need to be small. Teachers should have responsibility for no more than 80 students (about half the number most public high school teachers see in a day). And the choice of teaching materials and strategies is in the hands of the teachers and principal. Sizer sees teachers as coaches who provoke students to learn how to learn, not by lecturing but by probing, asking questions, making suggestions. This process, Sizer explains, means that the student must exert real effort.

For their part, students master a limited number of skills and areas of knowledge rather than a vast array of "subjects." What those skills and areas of knowledge should be are determined locally, based on the needs of the school's population.

There are no "grade-levels," and promotion is accomplished when the student can successfully demonstrate -- in what the Coalition calls an "exhibition" -- that he or she has mastered the material included in the school's program. The "exhibition" may be a written paper, a laboratory experiment, responses to questions, any number of things.

The relationship between student and teacher is meant to be not only pedagogical but personal, with teachers often acting as counselors outside the classroom.

It is understood in all of this that a student entering secondary school is competent in reading and elementary mathematics. If not, Sizer suggests that the school "invest heavily . . . in teaching how to read. Get her or him . . . to have some success. If this implies one-on-one tutoring, as many literacy programs have shown, ways must be found."

The last, and probably most difficult principle to carry out, according to some educators who are trying to put it into practice, is budgetary. Sizer estimates that running an essential school should cost no more than 10 percent more than operating a conventional high school.