Like all psychoeducational batteries, the Wechsler Individual Achievement Test, Fourth Edition (WIAT-4) requires independent investigation and analysis. The publisher provides multiple theories to support interpretation of its reading measures. At the word reading level, the battery includes a new Phonemic Proficiency subtest that the publisher reported correlated relatively higher with word reading skills than more basic phonological measures. However, its explanation of word reading skills in the context of other important predictors, like vocabulary, has not been investigated. At the comprehension level, the publisher endorsed an expanded simple view of reading, where oral reading fluency skills mediate the effects of word reading and oral language skills on comprehension. Using structural equation modeling with correlations provided in the technical manual, these analyses investigated multiple hypotheses stemming from publisher-endorsed theories. Results conformed to much of the publisher's word level theories, but they were more equivocal at the comprehension level. Implications for WIAT-4 interpretation are discussed.