Secondary course assignment substantially determines a teacher's day-to-day work life, incentivizing them to realize their personal desires, which prior work shows tend to be working with more advanced students. Teachers have varying abilities to enact these desires, potentially due to their political capital, which is largely influenced by school-specific experience. Teachers with more challenging assignments may be more likely to be dissatisfied and exit their jobs, making course assignment an important issue within the current nationwide teacher shortage. The current work includes three interconnected studies that explore the process of within-school secondary teacher assignment, how teacher experience associates with course assignment, and how course assignment associates with teacher mobility outcomes. The first work is a qualitative interview study with 17 Southern California secondary school leaders, revealing that teacher seniority was explicitly and implicitly important in driving course assignment decisions, with more seasoned teachers generally realizing their preferences. The second study utilizes nationally representative teacher data for a multiple regression analysis, finding that more senior teachers are less likely to teach potentially undesirable courses, such as Algebra I and 9th grade, and that such assignments correlate with increased teacher mobility. The third study makes use of longitudinal data from North Carolina teachers over a 15-year period with a survival analysis, uncovering that teachers assigned to potentially desirable courses, such as 6th grade, 12th grade, and AP, were less likely to exit their schools, while those assigned to 8th grade were significantly more likely to leave. The combined undesirability of 8th and 9th grades implies a plausible teacher preference to avoid teaching 14-year-olds, who tend to have greater behavioral issues. I conclude with recommendations for combatting potential inequities in assignment that may pay dividends for teacher retention, student success, and student equity. [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.]