This study compared the learning effectiveness, speaking time length, communication competence, foreign language speaking anxiety, and cognitive loads of high and low English proficiency students playing the roles of both assessors and practitioners in a mobile-assisted language learning activity. This study integrated a concept-mapping application as a mind tool with an oral recorder application on tablets to support EFL learners speaking English. The system, named CMAS (i.e., the Concept Mapping-Assisted Speaking system), includes peer assessment and evaluation of concept maps at the end of each round of activities. After three rounds, the results indicated that the overall speaking effectiveness including appropriateness of vocabulary, pronunciation, intonation, fluency, grammar, and accuracy of the high proficiency students was significantly higher than that of the low proficiency students. The cognitive loads of the low proficiency students were higher than those of the high proficiency students. However, there was no significant difference between the length of speaking time of the two groups. There was no remarkable difference between the speaking anxieties of the two groups after the experiment. The CMAS benefited not only the high-proficiency students but also the low-proficiency students, especially in terms of the speaking time length and the speaking anxieties of the low-proficiency students so future research directions were identified based on the results.