An operant preferential looking (OPL) test with random dot stereo targets was used to gather developmental data on stereoacuity thresholds in 180 children between 18 and 65 months of age. Results indicated a steady improvement in stereoacuity with age from 250 sec arc in the youngest children tested to 60 sec arc in the oldest group of children. The greatest improvement in stereoacuity occurs at 30 months of age where mean values improve from 225 to 125 sec arc. This large change in stereo threshold appears to be attributable to the significantly higher variability in responses in the children under 30 months of age vs. the lower variability in responses in children over 30 months of age. The overall steady improvements in stereoacuity appear to be a result of the developmental changes in the variability of responses rather than actual neurophysiological changes within the visual system.