Previous studies have demonstrated that making annotations can be a meaningful and useful learning method that promote metacognition and enhance learning achievement. A web-based annotation system, Virtual Pen (VPEN), which provides for the creation and review of annotations and homework solutions, has been developed to foster learning process among students. In order to explore the effects of reviewing annotations and homework solutions on learning achievement, a quasi-experiment was conducted with VPEN in a math class over a period of 4 months. It was found that reviewing own text annotations has a significant influence on learning achievement; while on the contrary, reviewing peers' text annotations has no significant influence on learning achievement. Our results show that students gain more from reviewing their own annotations than from reviewing the annotations made by peers, a contrast which reveals that annotations hold additional meaning for their creators. Further investigation revealed that only the quantity of text annotations among all other variables can significantly predict students' learning achievement. This finding may suggest that text annotations play more important roles to learning achievement than other variables, like homework. The reason is because text annotations are created by learners actively on voluntary base whereas homework is usually assigned by the teachers. Based on our findings, we suggest that teachers may consider incorporating learning activities that can foster metacognitive development into the learning process, like making annotations, solving homework and reviewing them, whereas peer learning should be encouraged only for reviewing the homework solutions of their peers with good learning achievement.