This study examined the meaning of flexibility in teaching at the postsecondary level and its connection to teaching effectiveness. A total of 500 college students and 15 instructors participated. Data were gathered using an online survey with open-ended questions for the students and one-on-one interviews with instructors. Analysis followed a grounded theory approach. Findings indicated that both students and instructors believed that when an effective teacher is also flexible, student learning improves. Considered as a crucial component of teaching effectiveness, flexibility in teaching is closely associated with a teacher's metacognitive reflection on student learning.