In this study, I investigated Grade 4 and 5 students' emotions while they engaged in the exploration of unsolved mathematics problems, including parts of the Graceful Tree Conjecture. Ten students from an after-school program in the Midwest participated in seven task-based interviews. The students exhibited a variety of emotions throughout the study, with frustration and joy displayed most frequently. I found the interplay of these emotions, joy and frustration, to describe the productive struggle that the students experienced while working on parts of the unsolved problems. A descriptive case of two students, Bernice and Alia, are included to describe how the interplay of frustration and joy characterize productive struggle. [For the complete proceedings, see ED606531.]