This study examines whether a Role Play Game (RPG) with embedded geological contents and students' anticipation of an upcoming posttest significantly affect high school students' achievements of and attitudes toward geology. The participants of the study were comprised of 202 high school students, 103 males and 99 females. The students were divided into four groups: (1) RPG group with pre-announced posttest; (2) RPG group with unannounced posttest; (3) No RPG group with pre-announced posttest; and (4) No RPG group with unannounced posttest. A 2x2 MANCOVA was conducted on the posttest scores with students' pretest scores as the covariates. The results indicated that: (a) there was no statistically significant interaction effect between RPG and anticipation of posttest on students' learning outcomes; (b) there was no statistically significant main effect for RPG on students' learning outcomes; however, (c) whether or not students had anticipated an upcoming posttest significantly affected their geological achievements and attitudes. In conclusion, testing has positive effects as a reinforcement to help students both retain their content knowledge and have positive attitudes towards geology.