Students' expectations about a class (their 'frames') affect how they interpret, approach, and accomplish tasks. However, little is known about students' framing of lab activities. During the first lab of a sequence designed to teach students about modeling and critical thinking with data, students test a simple model of a pendulum that breaks down with improved measurements. Using in-lab video and follow-up interviews, we identified students' frequent use of a model-verifying frame that substantially interferes with the instructional goals. We present an analysis of two students who approach the lab with a model-verifying frame and later shift their frames to accommodate goals aligned with instructional intention. As instructors transition labs to open-inquiry experiences, an activity that directly challenges the model-verifying frame may be productive for shifting students to frames that support their engagement in authentic experimentation.