What is the science of reading? The Reading League, in their document "Science of Reading: Defining Guide" (TRL, 2022), proposes that "The science of reading is a vast, interdisciplinary body of scientifically-based* research about reading and issues related to reading and writing." (p. 11.) The asterisk is carrying a lot of weight here. What does it mean for something to be scientifically based? It means that the evidence for a claim is weighed by the design and methods used to collect and analyze it, and the claim takes into account the limitations of that evidence. In this paper we will discuss some of the designs and methods used to investigate how children learn to read for understanding and provide a brief history into the use of these designs in reading and educational research. [This paper was published in "The Reading League Journal" Jan-Feb 2023.]