The relatively little amount of time that some college students spend reading their textbooks outside of the classroom presents a significant threat to their academic success. Using Prenksy's (2001) digital game-based learning (DGBL) principles and Astin's student involvement theory as frameworks, the purpose of this true experiment was to determine whether a significant difference in engagement, as indicated by mental effort and time on task, existed between college students who used a digital game-based textbook and students who used a traditional print-based textbook. A customizable digital game-based textbook designed using DGBL principles in a popular gaming genre embedded with textbook content identical to content in a traditional print-based textbook was used. Fifty-four undergraduate college students were randomly assigned to experimental and control groups. The results showed a statistically significant, Hotelling's T[superscript 2] (2,52) = 25.11, p<0.001, D[superscript 2] = 1.86 difference in engagement between participants in the experimental and control groups and a large overall effect size. Post hoc analyses indicated the digital game-based textbook group, exerted significantly greater mental effort (t = 2.38, p<0.001, d = 0.65) and spent significantly more time on task (t = 4.61, p < 0.025, d = 1.25) than the traditional print-based textbook group.