Policymakers are revolutionizing teacher evaluation by attaching greater stakes to student test scores and observation-based teacher effectiveness measures, but relatively little is known about why they often differ so much. Quantitative analysis of thirty schools suggests that teacher value-added measures and informal principal evaluations are positively, but weakly, correlated. Qualitative analysis suggests that some principals give high value-added teachers low ratings because the teachers exert too little effort and are "lone wolves" who work in isolation and contribute little to the school community. The results suggest that the method of evaluation may not only affect which specific teachers are rewarded in the short term, but shape the qualities of teacher and teaching students experience in the long term.