Despite strong universal starting points, striking individual differences in number sense emerge early in life and are present by the time children enter preschool (e.g., Klibanoff et al., 2006). These differences are apparent both on standardized tests (e.g., Arnold et al., 2002; Starkey, Klein, and Wakeley, 2004) and on specific measures tapping early number competencies, such as determining set size, comparing sets, and carrying out calculations (e.g., Entwisle and Alexander, 1990; Ginsburg and Russell, 1981; Griffin, Case, and Siegler, 1994; Jordan, Huttenlocher, and Levine, 1992; Levine et al., in preparation; Saxe, Guberman and Gearheart, 1987). The level of number sense in kindergarten is highly of predictive future mathematics success in first through third grades (Fuchs et al., 2007; Jordan, Glutting, and Ramineni, in press; Locuniak and Jordan, in press; Mazzocco and Thompson, 2005) as well as into the later school years (Duncan et al., 2007).

In this chapter, we explore individual differences in children’s mathematics competence. We begin by describing the differences associated with key social groups specifically defined by socioeconomic status, gender, race/ethnicity, and English language ability. We then discuss the contextual factors and early experiences that appear to be linked to these differences, giving particular attention to the role of the family and language. We then discuss learning disabilities. We end with a brief discussion of potential intervention.

Researchers have explored several key social factors that are linked to systematic, average differences in children’s mathematical performance. Socioeconomic status (SES), which includes income level as well as level of parental education, is strongly linked to differences in mathematics competence. Evidence related to gender differences in mathematics competence is less clear, although some differences have been found.

Mathematical skills of young children from low-income families lag behind those of their middle-income peers. Preschoolers who attend Head Start Programs perform significantly below children who attend preschools serving middle-income children on standardized tests of mathematical readiness (Ehrlich and Levine, 2007). The gulf between low- and middle-income children is wide and includes spatial/geometric and measurement as well as number competencies (Clements, Sarama, and Gerber, 2005; Klein and Starkey, 2004; Saxe et al., 1987).

Jordan and colleagues (Jordan et al., 2006, 2007) found that low-