Little is known about what contributes to individual differences in reading fluency after accounting for accuracy. Previous research has shown individual differences in the relative growth in word and nonword reading, specifically a pattern in which students who start lower on reading grow more in word than nonword reading ability. The purpose of the present study was to test whether this asymmetric growth contributes to individual differences in reading speed. Results showed that the relative growth in untimed word reading accuracy to untimed nonword reading accuracy from 1st to 4th grade contributed significantly to the prediction of 4th grade word reading efficiency after controlling for word reading accuracy. Specifically, those who grew more in untimed word reading accuracy than untimed nonword reading accuracy from 1st to 4th grade were slower readers compared to others with the same current accuracy levels. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]