The authors of the No Child Left Behind (NCLB 107-110) Act of 2001 anticipated that a majority of school districts or schools would not be able to attain state and national achievement standards without assistance. Consequently, the Act created a major tenet known as Supplemental Educational Services (SES) programs to improve the learning outcomes of students placed 'at-risk' and to hold public schools accountable for increasing the proficiency levels of students in reading and mathematics. This study examined whether provision of supplemental educational services significantly improved academic achievement of selected third, fifth, and eighth grade students in Baltimore City Public Schools after they received supplemental services. A quasi-experimental research design was utilized in this study to compare SES participants and non-participants. Consistent with a quasi-experimental design, subjects were not randomly assigned to treatment groups. The experimental groups are students who participated in SES, and the comparison groups are students who did not participate. The results of the study showed that the level of student participation was correlated significantly and positively with students' 06-07 MSA reading and math scores when their 05-06 MSA reading and math scores were controlled. School level showed a significant influence on the level of participation of students during the 2006-2007, and students who went to schools that met Adequate Yearly Progress (AYP) showed a higher level of participation than students who were in schools that did not meet AYP. A major implication in this study is that while correlations coefficients shown were statistically significant, they were often quite small. For instance, a positive and statistically significant correlation was found between hours of participation and MSA score; however, the correlation coefficients were small. As is well known, small correlations can become statistically significant as N (i.e., sample size) grows large. In this case, an N of over 2,000 cases enabled a small correlation to be statistically significant. It is difficult to assess whether the correlations found are behaviorally or socially significant enough to be a basis for major policy recommendations.