New York legislators made strides in improving teacher quality last year when they voted to require that probationary teachers show how they successfully use school data in shaping classroom instruction. In a disturbing step backwards for the state, the state assembly, after lobbying by teacher unions, voted last week to prohibit the use of student data when deciding if teachers should be awarded tenure.

Far too often, tenure is merely a step towards near-permanent job security, regardless of teacher effectiveness. It also arrives too soon in a teacher's career for sound, informed judgments to prevail. New York is one of 28 states that allow teachers to gain tenure in three years; 13 other states allow tenure to be granted after two years.

Instead of banning the use of student data, state leaders should further expand its use to assess the performance of tenured veteran teachers. Policymakers should also look to states such as Florida or Tennessee, which are successfully incorporating such information into teacher performance reviews.