In this study, we investigated the effects of individualized learning adapted to students' conceptions using smart devices in science instruction upon students' conceptual understanding, the retention of conception, achievement, learning motivation, enjoyment of science lessons, and perception about individualized learning using smart devices. Four seventh-grade classes at a coed middle school in Seoul were assigned to a control group and a treatment group. Students were taught about molecular motions for seven class periods. Two-way ANCOVA results revealed that the scores of a conception test, the retention of the conception test, a learning motivation test, and an enjoyment of science lessons test for the treatment group were significantly higher than those for the control group. Although the score of the treatment group was higher than that of the control group in the achievement test, the difference was not statistically significant. Students' perceptions about individualized learning using smart devices were also found to be positive.