Many studies have shown that morphological knowledge has effects on reading comprehension separate from other aspects of language knowledge. This has implications for reading instruction and assessment: it suggests that children could have reading comprehension difficulties that are due to a lack of morphological knowledge, and thus, that explicit instruction of morphology might be helpful for them, indeed for all children. To find children who might especially benefit from specific instruction in morphology, we would need good tests of morphological knowledge. We evaluated a set of morphological awareness assessments to determine whether they conclusively tapped into morphological knowledge, and found that it was not possible to be certain that they were accurately targeting morphological knowledge.