The usual "business school" approach to preventing metrics from causing unintended effects is to assemble a balanced scorecard of a dozen or metrics. If you do it right the negative factors of each cancel each other out. So for example to evaluate public school teachers instead of just looking at student improvements in standardized test scores relative to their peers you could also factor in subjective (but quantified) ratings from principals / students / peers, number of continuing education credit hours, student participation levels in extracurricular programs, counts of "suggestion box" ideas, etc.

http://www.balancedscorecard.org/Resources/About-the-Balance...