This study investigated the effects of using coloured filters on reading speed, accuracy, and comprehension as well as on perception of academic ability. A double-masked, placebo-controlled crossover design was used, with subjects being assessed over a period of 20 mo. There were three treatment groups (Placebo filters, Blue filters, and Optimal filters) involving 113 subjects with "reading difficulties", ranging in age from 9.2 yr. to 13.1 yr. and with an average discrepancy between chronological age and reading age of 1.8 yr. The 35 controls (who did not use coloured filters) ranged in age from 9.4 yr. to 12.9 yr., with an average discrepancy between chronological age and reading age of 2.1 yr. The treatment groups increased at a significantly greater rate than the control group in reading accuracy and reading comprehension but not for speed of reading. For self-reported perception of academic ability, two of the three treatment groups showed significantly greater increases than the control group. The larger improvements for treatment groups in reading comprehension may be related to a reduction in print and background distortions allowing attention to be directed to the processing of continuous text rather than to the identification of individual words. A reduction in print distortion, however, may not be sufficient to generate improved word-identification skills without additional remedial support, and this may be indicated by the nonsignificant increase in rate of reading.