Several states have recently adopted or are pursuing policies that deny or revoke tenure from teachers who receive poor evaluation ratings over time based in part on quantitative measures of performance. Using data from the state of Florida, we estimate such value-added measures to consider the future effectiveness and number of teachers who would have been dismissed under different versions of these policies. Students assigned to teachers who would have been dismissed according to a value-added policy made considerably smaller academic improvements than did students assigned to teachers who would have avoided dismissal. Critically, however, we show that specific policy design determines the extent of the potential for value-added to improve the overall quality of the teaching workforce.