As classes start today, I'm pleased to say that we don't have a single vacancy in my building. That is not the case at many schools around the country.

The retirement of thousands of baby boomer teachers coupled with the departure of younger teachers frustrated by the stress of working in low-performing schools is fueling a crisis in teacher turnover that is costing school districts substantial amounts of money as they scramble to fill their ranks for the fall term.

Superintendents and recruiters across the nation say the challenge of putting a qualified teacher in every classroom is heightened in subjects like math and science and is a particular struggle in high-poverty schools, where the turnover is highest. Thousands of classes in such schools have opened with substitute teachers in recent years.

Of course, there are ways of fixing the problem -- starting with higher salaries to entice more and better-qualified teachers into the classroom. Giving teachers more support instead of adopting the attitude that the student and parent are always right would help as well. Too many teachers I know walk away from the field in the first five years because they are imply beat down by the constant expectation that they accomplish miracles while standards of conduct and achievement are lowered for students. Until we see a return to the day when teachers were treated as respected professionals, the shortage will continue.