Purpose: School leaders are central to the development of work-related ties among school staff. Although prior work has examined the predictors of the presence of work-related ties, little is known about the breakup or dissolution of ties among school staff. This study examines the extent of tie dissolution among school staff, as well as both the individual- and organizational-level predictors of the breakup of ties. Research Methods: This study uses social network analysis of 4 years of survey data from 14 elementary schools in one suburban U.S. district. Social network models predict the likelihood of the breakup of a tie between school staff in three types of networks: close colleague networks, and instructional advice networks in mathematics and language arts. Findings: Work-related ties between school staff dissolve at high rates from year to year, and ties that dissolve generally do not re-form. Aspects of the formal school organization--particularly changing grade levels and losing leadership positions--predict the breakup of ties, while individual-level factors such as commitment to the school, perceptions of school leadership, and beliefs about instruction generally do not predict tie dissolution. Implications for Research and Practice: School leaders should carefully consider grade reassignments and changes in leadership positions, as these changes strongly predict the breakup of ties between school staff. School leaders should also invest in the promotion and maintenance of cross-grade ties after changes to grade-level assignments. [Appendix A and B are available in the online version of the article.]