Years of teaching experience have long been taken as an important indicator of teacher and school quality in primary and secondary schools. However, research on the effects of teacher years of experience on student outcomes has shown mixed results. To investigate the source of variation causing these mixed results, this study examined a broad range of student and classroom compositions that might affect the relationship between teacher years of experience and student outcomes, including standardized test scores in English Language Arts and Mathematics, Social-Emotional Test scores, and the count and severity of student disciplinary incidents. Using multilevel regression, this study analyzed longitudinal data obtained from the largest school district in the state of Arizona, Mesa Unified School District, which is classified as a mid-high poverty district. Despite the large sample size, a very weak and non-significant relationship was found for teacher years of experience on any student outcome. In contrast, student and family demographic backgrounds were significantly related to student outcomes. English and Math scores were significantly associated with student giftedness, home languages, and English learning status. Social-emotional test scores were significantly related to race/ethnicity, home languages, and special education status. Both discipline counts and severity were statistically associated with race/ethnicity, and gender, while special education status was significantly related only to discipline severity. In addition, classroom composition variables based on student and family demographics, and students' prior year scores on the outcome were significantly related to student outcomes. These results suggest that student characteristics, contextual classroom composition variables arising from student backgrounds are more important in predicting student outcomes than teacher years of experience, at least in a mid-high poverty school district. Therefore, student placements might be a key to addressing educational inequity for high-need students in mid-high poverty schools, consistent with prior studies in high-poverty schools. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]