Little research has examined the critical components of successful K-12 online schools, due in part to the theoretical focus of current frameworks on higher education rather than characteristics of K-12 online learners and environments. Using K-12 online research, this paper examined "teaching presence" as explained by the Community of Inquiry framework and identified additional teacher roles that needed stronger emphasis. We termed the new construct "teacher engagement." Teacher engagement was shown to be helpful in describing and identifying effective teacher practices at the Open High School of Utah (OHSU), a successful online charter school. Through a series of 22 interviews with over half of the OHSU faculty, it was found that teachers worked to improve student outcomes by (1) designing and organizing learning activities, (2) facilitating discourse with students and parents, (3) providing students with one-on-one instruction, (4) nurturing a safe and caring learning environment, (5) motivating students to engage in learning activities and (6) closely monitoring student behavior and learning. These six elements describe the core of "teacher engagement."