A study examined the effects of controlled language ("primerese") on children's reading. Four primerese stories from basal readers were rewritten to make the language less controlled and more natural, and the effects of these changes on several aspects of oral reading and comprehension were examined. Sixty first graders were divided into high and low ability groups based on ability to recognize individual words from the stories and were randomly assigned to groups that read either the original or the rewritten versions of the stories. Results indicated that regardless of text version, children with higher word recognition scores read at significantly faster rates and made fewer word miscues than children with lower word recognition, and also that those miscues they did make were more likely to be syntactically appropriate and less likely to be graphically similar to the printed word. In general, the language differences between original and rewritten versions did not significantly affect reading rate, word miscue rate, or proportion of graphically similar miscues. However, the children who read the rewritten versions tended to have significantly higher proportions of word miscues that were syntactically appropriate or that preserved meaning and also made fewer punctuation miscues and gave more correct answers to comprehension questions. These results suggest that primerese language discourages knowledge-based, top-down processing, and encourages more text-based, bottom-up processing instead, and that the disadvantages of primerese become more pronounced as young readers develop in their ability to recognize individual words and to process natural language in a fluent, top-down fashion. (Twelve tables of data are included and 35 references are attached.) (Author/SR)