This paper shares findings from the study of a learning sequence designed to support prospective elementary teachers (PTs) in identifying evidence of conceptual understanding and procedural fluency. Conceptual understanding and procedural fluency are widely recognized as important to teaching and learning mathematics, and identifying evidence of each is emphasized on teacher candidates' high-stakes performance assessments. As PTs practiced selecting evidence from student work samples, our analysis revealed successes as well as associated challenges. Our findings suggest areas for supporting PTs' learning, as well as challenges stemming from the inherent overlap of these two knowledge types. This study raises important questions about the value of emphasizing PTs' ability to cite evidence of conceptual understanding and procedural fluency, given their integrated nature.