FIFTY STUDENTS from some of D.C.'s poorest elementary and junior high schools just spent two weeks in intensive chess camp. Chess, as a number of other localities have already found, turns out to be an unexpectedly effective way to teach disadvantaged inner-city children to improve their concentration skills and their interest in schoolwork and to begin thinking of themselves as smart kids who can win at something intellectual. Not all are good at academics to begin with, and some, as in Philadelphia, have been chosen specifically because they were likely to drop out. But similar results have been reported for all of them, and substantial numbers stay in school who were not expected to do so. The D.C. version of these efforts, sponsored by the International Educational Network, was more modest. A lawyer named David Mehler went around to some schools drumming up interest and then taught the game to all 50 who expressed it at a cost of about $10,000. But this program is the opening move in a more ambitious initiative dubbed "Chess for Drug-Free Schools and Crime-Free Streets," being launched by, of all people, Soviet world chess champion Gary Kasparov. He visited Washington in February and got some funding from private foundations and government antidrug programs. True, those involved say part of the magic is the special nature of the game and the lessons it imparts -- in particular, the lesson that each move has consequences and changes the overall situation, and the habit of visualizing what that situation will be, and what the other player might do, before you make your move. Mr. Mehler, an instructor of some local renown, also likes to stress that in chess you always start even, that it's great to win and that, if you don't, you can set up the pieces and try again. It's similar to other programs that have worked not by giving disadvantaged students remedial work but by throwing at them academically rigorous and prestigious goals -- like advanced placement courses or calculus, as in the saga of Los Angeles teacher Jaime Escalante, the basis for the movie "Stand and Deliver." Kids learning calculus or chess and succeeding at it suddenly have a whole new building block in their mental self-image -- one that can serve as a foundation for the effort on which further attainments must rest.