Research Findings: In each of 16 public school classrooms serving multiethnic low-income neighborhoods, 2 first graders were assigned to be taught patterning, 2 to be taught reading, 2 to be taught mathematics, and 2 to be taught social studies for 15-min sessions 3 days per week for 6 months. Assignment within each classroom was randomized. The children's mean age was 6 years, 5.19 months. Patterning instruction included instruction on symmetrical patterns, patterns with increasing numbers of elements, and patterns involving the rotation of an object through 6 or 8 positions. In May, the 120 children still available were tested on patterns, reading, and mathematics. Patterning instruction had large, fully mediated effects on both reading and mathematics. There were no significant differences on some individual scales, but on others children who received patterning instruction scored best, often by grade equivalents of 4 to 8 months. Extant explanations of the efficacy of patterning instruction are reviewed, and the potential importance and limitations of its role in early education are discussed. Practice or Policy: Patterning instruction should be extended to more complex patterns than the alternations currently used in elementary schools in order to produce important improvements in both reading and mathematics.