Vision screening for young children can detect conditions that may lead to amblyopia and vision loss if left untreated. Portable vision screening devices with high levels of precision are now available, but their effectiveness in busy primary care settings is unknown. We analyzed the effect of deploying instrument screening devices (SPOT Vision Screener, Welch-Allyn) in 19 pediatric practices. At baseline, using chart-based screening, 65.3% of 3- to 5-year-old children completed screening. A significant increase was observed starting 3 weeks after delivery of devices, and a stable level was reached 12 weeks after implementation, with 86.5% of children completing vision screening (P = .007 by interrupted time series analysis). Improvement was greatest among 3-year-olds (44.0%-79.8%) but was also seen among 4-year-olds (70.9%-88.4%) and 5-year-olds (80.3%-90.8%). The deployment of vision screening devices in primary care practices substantially improved completed screening among preschool-aged children.