Purpose: Share a comprehensive examination of best practices used to institutionalize a successful long-term secondary education co-teaching program. Methodology: An intrinsic case study of a single urban school site in the Southern California area, bounded in time from program inception through the study time period. Findings: (a) Two visions dominated program adoption: respond to legal mandates and improve academic and social success of students with mild to moderate disabilities; (b) Formal co-teaching training was provided; (c) Absence of common planning time was a program barrier; (d) Finding and/or sustaining general education co-teachers was a program barrier; (e) Special education co-teachers should have or acquire course content knowledge; (f) Schools should slowly develop co-teaching programs; (g) Adaptive leadership was apparent; (h) Collaboration is an essential co teaching team process; (i) Trust, respect, and willingness to work together are necessary prerequisites for effective co teaching collaboration; (j) Co-teacher parity is a component of co-teacher leadership; (k) Co teaching improves student support; (l) Special education paraprofessionals are integrated into co-taught classes; (m) All interviewees reported positive co teaching efficacy; and (n) Interviewees foresaw or presumed long-term program existence. Conclusions: (a) Alignment with a co teaching best practices remains a school priority. (b) The co teaching program is likely to continue generally in its current form through the long term. Recommendations: (a) Utilize co teaching best practices with co teaching program implementation or modification; (b) expect general educators to proactively build differentiation knowledge; special educators to proactively build content knowledge; (c) do periodic environmental scans to identify co-teaching program priorities; (d) appoint an experienced co teacher to serve as a support staff advisor; (e) include co teacher representation in the co teacher hiring process; (f) among co-taught students with disabilities, expect immediate improvements in social skills; longer-term improvements in academic accomplishments; (g) special education teachers co-teach with no more than two general educators; general education teachers co teach with one special educator per content preparation; (h) maintain effective, voluntary co teaching team integrity; (i) assign selected special education classroom assistants to co taught classes with enrolled students who have more moderate disabilities and would otherwise be in self-contained classes; and (j) develop and implement a co teaching program-level evaluation system. [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.]