The present research represents a test of the effect of adding seriation instruction to oddity instruction to produce an advantage in both forms of abstraction. Pasnak et al. (2007) and Kidd, Pasnak, Gadzichowski, Ferral-Like, & Gallington (2008) have shown that at risk kindergartners profit academically from instruction in both oddity and seriation. This study extends this work into the preschool classroom, testing whether oddity and seriation instruction benefits at risk preschoolers in both literacy and numeracy. The research was conducted in seven Head Start preschools in Alexandria, Virginia, an urban community just south of Washington DC. That the literacy and numeracy control lessons were effective is shown by the high scores the children in those groups made in the specific domain in which they were instructed, However, the children who received the literacy or art instruction scored below national norms on numeracy, and the children taught numeracy or art likewise scored below norms on literacy, despite the enrichment offered by their Head Start program. Such outcomes are likely when children have been raised in impoverished homes. Lacking the cognitive enrichment that would be found in many middle-class homes, they were probably functioning closer to the floor provided by their inherent abilities than to the ceiling. At least, that is one of the assumptions on which this research was based. Lagging in normal cognitive development, they would be less apt to understand and profit from preschool activities aimed at fostering literacy and numeracy. That the cognitive group matched the numeracy group in numeracy, and the literacy group in literacy, testifies to the importance of the advantages in abstraction that group had gained. These advantages appear to have enabled it to better understand the normal preschool curriculum, which offered plenty of chances to improve on literacy and numeracy. Preschool learning activities assume that children can detect relevant differences and understand the relations between big, medium, small, and so forth. When children are deficient in these abstractions, many of the instructional activities are over their heads. The authors conclude that strengthening children's understanding of differences on one dimension and unidimensional ordering enables them to gain more from learning opportunities in the preschool classroom.