An understanding of statistics and skills in data analysis are becoming more and more essential, yet research consistently shows that students struggle with these concepts at all levels. This case study documents some of the struggles four groups of fifth-grade students encounter as they collect, organize, and interpret data and then ultimately attempt to draw conclusions or make decisions based on these data. The activities in which the students engaged were part of an integrated science, technology, engineering, and mathematics (STEM) unit that had students collecting and analyzing data both in the context of learning science concepts and in the context of evaluating prototypes for an engineering design challenge. Students were observed to struggle in a variety of ways, specifically having difficulty (1) properly using certain measurement devices, (2) coordinating quantitative data with the phenomenon being measured, and (3) properly interpreting the significance of variation, uncertainty, and error in the data. Implications for teaching and curriculum design are addressed.