Quantitative Undergraduate Biology Education and Synthesis (QUBES) is an NSF funded project with the mission to improve learning opportunities for all students enrolled in undergraduate biology courses by reflecting the centrality of quantitative approaches in modern biology. We will provide an overview of the QUBES project, then discuss the Quantitative Modelling assessment QM BUGS. The diagnostic assessment and associated RTOP observation protocol have been administered in biology classes at two universities. The assessment consists of 30 questions on quantitative modelling ability and student confidence about modelling. We will report the findings from a pilot administration in Fall 2017 and discuss revision of the assessment informed by Rasch Analysis.