Reinterpreting the development of reading skills

Theories about reading have neglected basic differences in the developmental trajectories of skills related to reading. This essay proposes that some reading skills, such as learning the letters of the alphabet, are constrained to small sets of knowledge that are mastered in relatively brief periods of development. In contrast, other skills, such as vocabulary, are unconstrained by the knowledge to be acquired or the duration of learning. The conceptual, developmental, and methodological constraints on different reading skills are described in this essay that identifies various types of constraints on reading constructs and measures. Examples of reading research and assessment are discussed to illustrate (a) how the constraints can help to explain transitory correlational patterns among reading data, (b) how proxy effects surrounding constrained skills influence interpretations of reading development, (c) how prescriptions to teach constrained skills are causal misinterpretations of longitudinal correlations, and (d) why interventions on constrained skills usually lead only to temporary gains on skills aligned with the constrained skill. Because constrained skills are not normally distributed conceptually or empirically, except on special occasions, analyses based on parametric statistics are inappropriate. This essay describes implications for theories of reading development, research methods, and educational policies.