This study tests a model that predicts the problem-posing performance of sixth-grade students (independent variable metacognition, mediator variables mathematics and native language course success scores at the end of the year). The research was conducted with the relational model. The results regarding the mediation effect indicated that the mathematics course success scores and the native language course success scores were separately full mediators in the effect metacognition has on problem-posing performance. The results regarding serial mediation effect revealed that the mathematics course success scores and native language course success scores had a full mediating effect on the effect of metacognition on problem-posing performance.