Across the country states and school districts need to improve the mathematics performance of students with disabilities. This population of students increased since the 1970s, and there have also been changes in education expectations and accountability under the requirements of the Individuals with Disabilities Education Acts of 1997 and 2004 and the No Child Left Behind (NCLB) Act of 2001. NCLB, in particular, has cast light on the generally low mathematics performance of many students with disabilities and on the achievement gaps between this subgroup and general education students. Performance trends in the Northeast and Islands Region mirror those of the country. This report presents descriptive and inferential analyses of mathematics achievement patterns for grade 4 students with disabilities and general education students in Massachusetts. Three research questions are examined: (1) What is the mathematics performance of public school grade 4 students with disabilities in Massachusetts? (2) How has the performance of grade 4 students with disabilities and grade 4 general education students changed over time? and (3) What is the gap in proficiency percentages between grade 4 general education students and grade 4 students with disabilities? The report finds that in 2006, 15.3 percent of grade 4 students with disabilities reached proficiency on the Massachusetts Comprehensive Assessment System exam. The performance of students with disabilities differed across the locale-need combination categories. The proficiency gap between general education students and students with disabilities reflected decreases in proficiency among both groups, with general education students falling more. The gap shrank in low- and medium-need schools in both suburban and rural locales. But the gap widened in high-need schools across all locales and in urban schools across all need categories. The report illustrates the analyses that state and district leaders can conduct with publicly reported data, along with the ways the findings can be interpreted. The limitations of the analyses come from examining cross-sectional data on the proportion of students scoring proficient rather than longitudinal data on actual student scores, and from lacking information on the types and severity of disabilities. The findings and limitations are important as states move forward in analyzing subgroup performance and proficiency gap data and in making data-driven decisions. Data Sources and Methods are appended. (Contains 2 endnotes, 3 boxes, 7 figures and 8 tables.) [This report was prepared for the National Center for Education Evaluation and Regional Assistance, Institute of Education Sciences, U.S. Department of Education by Regional Educational Laboratory Northeast and Islands administered by Education Development Center, Inc.]