Understanding the relationship between teacher test scores and student achievement is important in an accountability environment that favors using quantitative measures of teaching quality, as is the case with Mexico's national "Carrera Magisterial" (CM) teacher incentive program. The results of this paper suggest that teacher test scores have a small positive relationship with average student achievement scores. This effect is larger in secondary schools than in primary schools. In the case of secondary schools, average teacher test scores on subject-matter and teaching methodology sections of the test are positively associated with student achievement. To estimate these relationships this paper uses panel data from Mexico's national teacher incentive program CM from 1996 to 2000.