The granting of tenure typically occurs after K–12 teachers have worked three years in the classroom. In many places, that’s it, just time-in-harness. Thankfully, however, some states do require that teachers meet specific benchmarks relative to student test performance or classroom observation scores. One would imagine that the latter would be preferable, but a recent study out of Tennessee puts that notion to the test: Does lengthening the tenure process, coupled with a measure of minimum effectiveness, improve teacher performance? Tennessee’s approach to tenure provides a natural experiment by which to investigate that question.