This study developed a new survey of teachers' knowledge about early reading and examined the effects of teachers' knowledge on students' reading achievement in Grades 1 to 3 in a large sample of Michigan schools. Using statistical models that controlled for teachers' personal and professional characteristics, students' prior reading achievement, and the clustering of high-knowledge teachers in schools and school districts with particular demographic composition, we found that the effects of teachers' knowledge about early reading on students' reading achievement were small. In 1st grade, students in classrooms headed by higher knowledge teachers performed better on year-end tests of reading comprehension but not word analysis. In 2nd and 3rd grades, the effects of teachers' knowledge on either measure of students' reading achievement were not statistically significant. Although the study suggests new forms of statistical analysis that might produce better estimates of the effects of teachers' knowledge on students' reading achievement, further research is needed to improve the conceptual and psychometric properties of measures of teachers' knowledge of reading and to investigate the relation of their knowledge and their instructional practices. (Contains 2 figures, 6 footnotes, and 6 tables.)