This study tested the hypothesis that music training causes improvements in several diverse aspects of cognition, and that one way music training produces these effects is by improving attention. We tested this hypothesis using a “pre-post” intervention study design, in which we measured children’s test scores at baseline, prior to the intervention, and again following the intervention. We enrolled a total of 88 children from Head Start preschools. All were three-to-five years old, from low socio-economic status (SES) families, right handed, monolingual English speakers, and free of neurological or behavioral disorders. The children were randomly assigned to be in either regular Head Start or in one of three smaller groups. Each small group met for instruction within the regular class time for 40 minutes per day, five days per week, over an eight-week period.