Prompted by current theories in reading suggesting that variation in word knowledge affects the processing of not only individual words but also clauses and sentences, this report explores some different ways in which children's comprehension processes may be affected by variation in word knowledge. The report first examines whether the effects of word knowledge on comprehension are similar for skilled and less-skilled readers, then compares how well stories containing unfamiliar versus recently taught words are remembered. It then considers various models of how comprehension processes may have been affected to produce the observed recall differences and evaluates them against experimental data. Finally, it presents some implications for theories of text processing, education, and the use of modelling as an experimental tool. (HOD)