Unified Modeling Language (UML) has been adopted as a standard modeling language in the software industry for the graphical representation of analysis and design models. Due to its importance, UML is taught in most undergraduate majors in Software Engineering and Computing. However, little is known about the students' perception regarding the UML diagrams. Their perceptions may influence the diagrams' adoption since the students are future software engineers. This paper aims to start filling this gap by better understanding students' perception regarding UML diagrams acceptance. To achieve this goal, we applied a Focus Group to foster a discussion with undergraduate students about five UML diagrams. Besides, we applied the Technology Acceptance Model to assess the students' acceptance regarding these diagrams. Based on the results of this study, students considered use cases and class diagrams useful for designing systems, although they stated that their modeling was not easy. We also noticed that the perceived usefulness was the construct that most influenced the students' intention to use these diagrams. Our research benefits instructors interested in understanding the students' perceptions about UML, enlightening the points that they need to reinforce to show the benefits of the modeling language. Still, the instructors are invited to reflect on other teaching strategies to show the importance of these diagrams in the software development process.