Research Findings: A total of 72 Head Start children (M age = 53.26 months, SD = 5.07) were randomly assigned to 4 conditions. Some were taught the oddity principle (choosing the object that differs from others in a group) and seriation (ordering objects on a dimension and inserting new objects into such orders), which are forms of thinking that develop naturally at about age 4. Others were taught letters or numbers or were engaged in art activities in sessions matched in frequency, timing, and extent. Toy animals were used as props in lessons that scaffolded the children's learning. Preschoolers in the cognitive group improved their cognitive skills significantly more than the others and also became better than the numbers or art groups at identifying letters, as measured by the Letters and Words scale of the Stanford Early School Achievement Test 2. This indicates that with improved oddity and seriation skills, children profited more from lessons and letter sounds offered to all children by their classroom teacher. Comparable results were demonstrated for the oddity and seriation instruction and progress in counting and adding and subtracting objects as measured by the Woodcock-Johnson III Applied Problems scale. Practice or Policy: The content and procedures embodied in this research enable children who are economically disadvantaged to make progress in learning letters and in numeracy when enrolled in preschool. Brief periods of such activities for most of the school year may be an effective supplement to lessons on letters, letter sounds, and numeracy offered in preschool curricula. (Contains 3 tables.)