Attending to the whole unit that a number refers to in a mathematical problem situation and showing flexibility in coordinating different units are foundational for mathematical understanding. In this study, we explored teachers' attention to and flexibility with referent units in situations involving fractions and fraction multiplication. Using data collected across the USA from 246 mathematics teachers in Grades 3-7 where fractions are taught, we found that teachers' attention to and flexibility with referent units were related to each other as well as to teachers' overall knowledge of fractions.