The body of research on teacher quality is, if nothing else, a mixed bag, in terms of both quality and approach. Studies of the effects of preschool education levels have employed techniques ranging from simple correlations to complex statistical analyses that seek to account for the complexities of interrelated policies and practices that affect teaching and learning. Given just how complex policy and practice are, it may be that the simple correlations are just as informative for policy purposes, but neither approach is particularly satisfactory.
Please visit National Institute for Early Education Research (NIEER) for the complete blog post.