This study examined mathematics achievement of fourth and fifth grade students in Mississippi and principals' perceptions of inclusion. A sample of 462 students from eight separate elementary schools was selected for this study. Fifteen principals completed the Principal and Inclusion Survey regarding inclusion education. Eight of the 15 principals were interviewed with 10 open-ended questions regarding their perceptions of inclusion. Data were analyzed using an independent two-tailed "t" test and Pearson product moment correlation. The independent two-tailed "t" test was used to determine differences in mathematics achievement for fourth and fifth grade students in inclusion classrooms compared to non-inclusion classrooms and by gender. Qualitative data were gathered for the eight principal interviews. Data were coded to analyze recurring themes throughout the interviews. Pearson product moment correlation was used to investigate a correlation between mathematics achievement and principal perceptions of inclusion. Results of the data analysis showed no significant differences at the 0.05 level in mathematics achievements between regular education students in inclusion classrooms compared to non-inclusion classrooms. Descriptives concerning the Principal and Inclusion Survey indicated that principal perceptions regarding inclusion were very similar. An independent two tailed "t" test showed a significant difference by gender of principals regarding appropriate placement for students with disabilities. Qualitative data resulted in four emerging themes regarding the eight principal interviews regarding their perceptions of inclusion. The themes that emerged from the data included: (1) roles and relationships of teachers in inclusionary practices; (2) parental involvement, knowledge, and respect for inclusion education; (3) principals' responsibilities in the conflicting nature of inclusionary practices; (4) the physical environment inclusive to learning for inclusion education. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.