Qualification and preparation standards for entering and remaining in the teaching profession have long been under fire from both inside and outside the profession.

Programs have been criticized for allowing too many unqualified candidates to enter professional training programs, and then permitting them to graduate without meeting not just standards of excellence, but falling short of mere adequacy.

In addition, many systems are said to keep underqualified teachers through tenure. The New York City system removes challenged teachers from the classroom, for example, but keeps them on the payroll for years while their cases are appealed.

And as Education Week magazine reported recently, the cutoff scores on teacher exams in many areas are set far below the average test-taker’s score, allowing many below-average teachers to qualify.

That’s why it’s heartening that one of the nation’s top two teachers’ unions has proposed a “rigorous professional examination” to become a teacher, similar to the bar exam lawyers must pass before they can practice.

The American Federation of Teachers says that its proposal, released this past weekend, would result in “raising the standards of the profession and making sure that kids got teachers that are prepared.”

It’s not just an exam, either. The AFT would require that teacher candidates have college averages of 3.0 or higher, and get relatively high scores on college or graduate-school entrance exams such as the SAT or the ACT.

Candidates would have to show mastery of the subject matter they wished to teach, and spend a year in “clinical practice” before taking the exam.

There are about 1,400 teacher training programs in the country, and standards vary widely. But, just as lawyers from any law school all face one exam, so should teachers, the AFT says.

The group favors letting states, not the federal government, adopt the exam because they control the current accrediting process.

The AFT’s rival, the National Education Association, has its own proposals for reforms that might dovetail with an exam, as well. The idea has great merit, but it won’t go anywhere without widespread acceptance.

Still, what would be a good reason to turn it down?