This study has three major purposes, including designing mobile natural-science learning activities that rest on the 5E Learning Cycle, examining the effects of these learning activities on students' performances of learning aquatic plants, and exploring students' perceptions toward these learning activities. A case-study method is utilized and the science club with 46 fourth-grade students is selected as the study case in the study. Besides, a set of quantitative and qualitative data were collected from the case to document the learning effects of and the students' perceptions of the learning activities, and to discuss factors underlying these effects and students' perceptions. The results indicate that the learning activities can enhance students' scientific performances, including both knowledge and understanding levels. Students' perceptions of these learning activities appear to be positive. The study identifies two factors that are prominent in the positive effects: students' engaging in "mobile-technology supported" observation during their scientific inquiry; and students' engaging in "mobile-technology supported" manipulation during their scientific inquiry. Finally, the conclusions that our study has drawn could constitute a useful guide for educational practitioners concerned with the potentials of mobile computing in school settings.