(FORTUNE Magazine) – Violence in the nation's public schools is rising, classrooms are overcrowded, and teacher salaries are under siege. Teachers' union officials say that such poor working conditions and low pay make teaching an unattractive profession. More than half (51.6%) of all teachers are over 40, up from 48.4% in 1988. The result, according to figures culled by the American Federation of Teachers, is a potential shortage of 310,000 teachers by the year 2001. Even the union agrees that somebody will take those jobs. Says AFT President Albert Shanker: ''We never send children home in the U.S. We just hire the next person down the list.'' Shanker wants to bring more highly qualified people into the profession by making the job more attractive. This would involve cutting down bureaucratic supervision, raising certification standards, and, yes, increasing salaries. But unions won't consider other ideas that would help reduce the threat of the shortage -- for instance, higher pay just for teachers who can earn more outside doing something else. Such a market-driven structure would help retain physics and math teachers, who leave the profession at a rate 60% higher than other teachers, according to David Grissmer, an education researcher at the nonprofit Rand Corp. Says he: ''If unions maintain a uniform payment structure, then whenever there's a shortage in a certain area, they can get pay increases across the board. I think in the end taxpayers understand, and don't support, that kind of wage system.'' -- R.T.

CHART: NOT AVAILABLE CREDIT: FRANK O'CONNELL FOR FORTUNE/SOURCE: AMERICAN FEDERATION OF TEACHERS CAPTION: THE TEACHER GAP