There is consensus that, for student achievement, teachers matter. However, providing reliable research evidence for the effects of observable teacher characteristics, such as qualification measures, has been difficult. The current study uses panel data based on register information from teachers and students to estimate effects of teacher characteristics on student achievement in mathematics and Swedish in Grade 6. Applying fixed-effects regression to a large sample of schools, we observed significant positive effects of several teacher characteristics. Having a teaching license was found to be one of the most important qualification measures, but teachers' level of experience was also important for student achievement. The effects of teacher qualifications were generally stronger for mathematics than for Swedish.