Background <p>A growing body of studies has shown that fundamental movement skills (FMS) and physical activity (PA) are crucial for preschoolers’ development. However, most Hong Kong preschoolers still do not meet the WHO guidelines for PA and demonstrate poor FMS performance. The present study examined the effectiveness of physical activity routines, education, assessment, literacy, and information technology application in young children (PA-REALITY), a social cognitive theory-based movement education program led by preschool teachers.</p> Methods <p>Twenty-nine preschools signed up for the program and were cluster-randomized into an experimental group (15 preschools) and a wait-list control group (14 preschools). Totally 440 (age = 4 ± 0.95 years; 54.5% male) preschoolers took part in the baseline test and 349 preschoolers from 26 schools took part in the post-test (10 months). We delivered intervention contents including teacher workshops, teaching materials (booklet, simple sports equipment), and a mobile application to teachers. At baseline and post-test (10 months), respectively, preschoolers’ FMS proficiency, PA, and executive function (EF) were assessed using objective tools. Mixed-linear models using intention-to-treat analyses were used to examine intervention effects.</p> Results <p>Participants in the experimental group showed significant improvements in catch (<i>B</i> = 0.37, <i>p</i> &lt; .001) and moderate-to-vigorous PA (<i>B</i> = 4.49, <i>p</i> = .04) at 10 months, compared with participants in the wait-list control group. No effects were found for total PA other FMS and EF outcomes.</p> Conclusions <p>The PA-REALITY intervention improved some FMS outcomes and MVPA at 10 months. These results highlight the important roles of teachers in developing children’s movement skills and PA. Continuous professional development training for teachers may be an effective and sustainable way to improve existing practices.</p>