A growing body of research suggests that comprehension of expository texts presented digitally is a challenging endeavor, particularly for children. Many reading interventions, both from traditional classroom settings and computer-based contexts, have focused on much needed strategy instruction but have simultaneously neglected a focus on motivation. Alternatively, game-based learning environments (GBLEs) have the potential to simultaneously address both motivation and strategy use. Currently, there are few available GBLEs that target expository text comprehension. For this reason, this study employed a quasi-experimental between-subjects media comparison design to examine the effects of Missions with Monty, a GBLE supporting metacomprehension for expository science texts, on reading comprehension and motivation. Fifth-grade students (N = 234) engaged with either Missions with Monty or a comparison, computer-based version of the program lacking gamified elements for a period of 6 weeks and were assessed on reading comprehension skills and five dimensions of reading motivation. Results indicated that students in the GBLE condition showed significantly greater improvements in reading comprehension (g = 0.56), intrinsic motivation for reading (g = 0.52), and curiosity (g = 1.11) than their comparison-condition peers. Moreover, effects of the intervention on reading motivation were independent of prior reading comprehension for each of the reading motivation dimensions except reading efficacy. These findings support the notion that GBLEs can be an effective tool to foster digital expository text comprehension, particularly for struggling and uninterested readers.