States and the federal government have invested in early care and education programs with an explicit goal of improving school readiness for low-income children. These investments, aimed at strengthening the quality of care and supporting families' access to high-quality settings, are based in part on a confluence of research findings showing a link between program quality and children's outcomes. The four goals for these analyses were to: (1) Estimate the magnitude of the association for preschoolers specifically from low-income families between widely used global measures of observed classroom quality and well-established measures of child outcomes; (2) Consider whether the associations between quality and child outcomes are stronger when specific aspects of quality are examined in relation to specific child outcomes, such as instructional practices and early academic achievement; (3) Test whether there is evidence of threshold effects in the classroom quality-child outcome association for low-income children, for example whether associations of quality and child outcomes are especially strong at certain levels of quality; and (4) Examine the association between individual items and child outcomes for two quality measures used extensively in state quality improvement initiatives. Using two complementary research strategies allowed the researchers to compare the findings and make recommendations based on a synthesis of results across the two approaches. Both sets of analyses described the extent to which measures of classroom quality predict children's academic achievement and language skills as measured by standardized individually administered tests and children's social-behavioral skills as measured by questionnaires completed by classroom teachers. Analyses controlled for background characteristics such as maternal education, ethnicity, and site to account for pre-existing differences in families related to which families select and can afford higher-quality care and thereby more fully focus on the link between quality and child outcomes. (Contains 10 footnotes.)