The writer calls attention to the many traps associated with one of the most frequent uses of assessment: the technical difficulties of measuring changes in learning over time. Noting that psychometricians don't like "change" or "difference" scores in statistical analyses because they tend to have lower reliability than the original measures themselves. Bond applauds educators who recognize that difference between what students know before instruction and what they know after instruction reveals important aspects of teaching and provides example from personal experience to support his conclusion that measurement and assessment should have a more prominent place in teacher education curricula.