This paper reports improvements in teacher job performance, as measured by student test scores, resulting from a program of (zero-) low-stakes peer evaluation. Teachers working at the same school observed and scored each other’s teaching. Students in randomly-assigned treatment schools scored 0.07σ higher on math and English exams (0.09σ lower-bound TOT). Within each treatment school, teachers were further randomly assigned to roles: observer and observee. Teachers in both roles improved, perhaps slightly more for observers. The typical treatment school completed 2-3 observations per observee teacher. Variation in observations was generated partly by randomly assigning a low and high (2*low) dose of suggested number of observations. Benefits were quite similar across dose conditions.