Review of research literature has led to the conclusion that it is the teacher, more than the material, the method, or any other variable, that makes the greatest difference in children's reading achievement. Measuring teacher abilities and effectiveness is, however, a difficult if not impossible task unless teaching is defined in terms of teacher behavior as related to pupil behavior and cognitive aspects of learning. Future research should be concerned with (1) formulating a broad and inclusive concept of reading maturity, (2) making decisions on how to measure correlates of reading growth, (3) ascertaining teacher characteristics and behavior which are most effective in promoting these assumed factors or variables, (4) subjecting each assumed factor to measurement and determining its relation to pupil growth in reading, and (5) using all of this information to improve programs of teacher education in reading. References are included. (MD)