This paper attends to challenges for postsecondary science education improvement initiatives, notably understanding and responding to the realities guiding educators' teaching practices. We explored 16 postsecondary biology educators' instructional planning, providing novel insights into why educators select certain strategies over others, including lecturing. Our findings point to an array of factors that educators consider, factors that we believe push against the lecture versus active-learning dichotomy that we hear in some improvement rhetoric. We recommend professional development experiences (including peer evaluations of teaching) wherein educators and other proponents for teaching improvements explicitly explore rationales for teaching, including educators' considerations of the nature of the discipline (content and concepts and skills and processes) and students' needs. Educators with less experience with content were more likely to seek out additional instructional resources during planning, including other educators. Given this, teaching improvement proponents may want to offer professional development activities that sync with periodic and planned teaching assignments that take educators out of their disciplinary knowledge comfort zone. Disciplinary colleagues might serve as exemplars of planning and implementing teaching strategies that both convey foundational content and processes and engage students via evidence-based practices.