Schools in America have used museums as resources to supplement their curriculum since the 19th century. Field trip research is predominantly from the teachers' and students' perspectives, and draws attention to teachers' and students' contributions prior to, during, and after their field trips. Meanwhile, museum educators' contributions to field trip experiences have been scantily addressed. These educators develop and implement programs intended to help students explore and make sense of their experiences, and despite their limited time with students, studies show they can be memorable. First, field trips are a break in the usual routine, and thus educators leading programs have curiosity and attention attracting power. Second, classroom science teaching literature suggests teachers' teaching knowledge and goals can affect their behaviors, and in turn influence student learning. Third, classroom teachers are novices at planning and implementing field trip planners consequently museum educators can share this responsibility.The follwing research questions guided this participant observation study intended to examine one aspect of the teaching culture in museums, i.e. instruction during one-time science lessons. (1) How do educators teaching one-time lessons in museums adapt their instruction to the students they teach? (2) How do time limitations affect instruction? (3) How does perceived variability in entering student knowledge affect instruction? Data included observations, interviews, and researcher field notes. An inductive analysis model was adopted to analyze the data. Five major findings emerged from this analysis. (1) Repeating lessons develop comfort and insight to compensate one-time nature of lessons. (2) Details within science lessons can vary according to the students. (3) A lifelong learning perspective forms the foundation for educators' choices. (4) Refine teaching to use time efficiently. (5) Educators designate roles to teachers and chaperones to maximize time. These findings had implications for museum educators, classroom teachers, and all those involved in school field trips. Recommendations for action and future research emerging from this study were listed and discussed.