This paper presents a study on implementing the ASR-based CALL (computer-assisted language learning based upon automatic speech recognition) system embedded with both formative and summative feedback approaches and using implicit and explicit strategies to enhance adult and young learners' English pronunciation. Two groups of learners including 18 adults and 16 seventh graders participated in the study. The results indicate that the formative feedback had a positive impact on improving the learners' speaking articulation, and the summative feedback aided the learners' self-reflection and helped them to track their speaking progress. Furthermore, the implicit information such as model pronunciation with full sentences and audio recast benefitted the adult learners, whereas the young learners preferred the explicit learning information such as textual information of individual words for self-correction. In addition, the results of this study also confirm that learners have different perceptions of the media modalities designed with implicit and explicit strategies in the feedback. Feedback with audio modality is more suitable for adults, whereas juxtaposed textual and audio modalities are better for young learners.