Programs that use multi-threaded concurrency are known to be difficult to design. Moreover, research in computer-science education suggests that concurrency and synchronization concepts are generally difficult to master. It stands to reason that comprehension tasks may be more complex for programs that employ concurrency than for sequential programs. We believe that external representations, specifically refinements to some of the popular UML modeling notations, should aid students in mastering fundamental concurrency/ synchronization concepts and should enable practitioners to better comprehend the dynamically evolving nature of the these programs. In this paper, we present our synchronization adorned UML (saUML) sequence diagram notation that highlights aspects of thread interactions and describe an empirical study of whether these diagrams, as opposed to purely textual representations, help students to better understand concurrent executions and concurrency concepts, as measured by their ability to answer questions about a particular execution of a multi-threaded system. A statistically significant benefit was found from the study.