  We demonstrate how students' use of modeling can be examined and assessed
using student notebooks collected from an upper-division electronics lab
course. The use of models is a ubiquitous practice in undergraduate physics
education, but the process of constructing, testing, and refining these models
is much less common. We focus our attention on a lab course that has been
transformed to engage students in this modeling process during lab activities.
The design of the lab activities was guided by a framework that captures the
different components of model-based reasoning, called the Modeling Framework
for Experimental Physics. We demonstrate how this framework can be used to
assess students' written work and to identify how students' model-based
reasoning differed from activity to activity. Broadly speaking, we were able to
identify the different steps of students' model-based reasoning and assess the
completeness of their reasoning. Varying degrees of scaffolding present across
the activities had an impact on how thoroughly students would engage in the
full modeling process, with more scaffolded activities resulting in more
thorough engagement with the process. Finally, we identified that the step in
the process with which students had the most difficulty was the comparison
between their interpreted data and their model prediction. Students did not use
sufficiently sophisticated criteria in evaluating such comparisons, which had
the effect of halting the modeling process. This may indicate that in order to
engage students further in using model-based reasoning during lab activities,
the instructor needs to provide further scaffolding for how students make these
types of experimental comparisons. This is an important design consideration
for other such courses attempting to incorporate modeling as a learning goal.
