Purpose: Previous research has suggested that the size of the visual span—the number of letters recognizable in a glance—imposes a fundamental limit on reading speed (Legge, Mansfield, & Chung, Vision Research, 41, 725-734, 2001). The present study investigates developmental changes in the size of the visual span in school-age children, and the potential impact on children's reading speed. Method: The study design includes groups of 10 children in 3rd, 5th, and 7th grade, and 10 adults. Two print sizes (0.25°, 1.0°) and two exposure times (100ms, 200ms) were used. To measure visual spans, participants were presented with trigrams (random strings of three letters) flashed briefly at varying letter positions (0 to 5) left and right of the fixation point. Over a block of trials, a profile was built up showing letter recognition accuracy (% correct) versus letter position. This profile was fit by a split Gaussian model, and the results were used to estimate the size of the visual span (area under the profile) for the four combinations of print size and exposure time. For each participant, visual acuity and reading acuity were assessed with the Lighthouse Near Acuity Test and MNREAD chart respectively. Results: Preliminary findings indicate that children have significantly smaller visual spans than adults (F (1, 72) = 14.66, p < 0.05). There was also evidence for increasing visual-span size across increasing grade level. We also found that 200ms exposure time yielded a larger visual span than 100ms. However, no significant print size effects or interactions among age, print size, and exposure time were found. Conclusion: These results show that there are significant developmental changes in the size of the visual span from grade school to adulthood. The findings are consistent with the view that the growth of the visual span plays a role in the development of reading speed in children.