On the assumption that word frequency in written language as well as children's knowledge of words can provide the basis for a systematic contextual approach to reading vocabulary development, six current reading series and their workbooks (grades two through six) were analyzed for their presentation of prefixed words in context. Results of the study revealed that sufficient opportunities for systematic vocabulary development did not exist at many grade levels in the series for the following reasons: there was a general lack of coordination between what was suggested for teaching in the teacher's guides and what was offered in corresponding reading selections; textbook writers and consultants misunderstood what prefixation is in the English language; and there was an over-reliance on the principle of frequency or on the literary selections in determining the vocabulary used in the text. It was concluded that a generalization from the findings on prefixed words justifies the development of a new rationale for determining vocabulary in reading texts. (MAI)