We aimed to investigate the impact of smartphone use during intertrial intervals within a distributed practice regime on mental fatigue, performance, and learning of a balance motor skill. One hundred and thirty-six participants were randomly divided into two groups: the smartphone use group (SMARTPHONE) and the control group (CONTROL). The SMARTPHONE accessed social media during the rest periods within a distributed practice of a balance task, whereas the CONTROL rested passively during the rest periods. The participants practiced the toe-touch task. The participants underwent a pretest consisting of one trial. Subsequently, the participants were engaged in practice, completing six trials interspersed with 2-min intervals of either rest or smartphone use. Following the practice phase, a posttest was conducted, and after 24 hr, we administered a retention test and a transfer test. The number of touches and the number of errors (contacting the ground with the free leg to regain balance) were performance measures. We evaluated the participants' mental fatigue after the practice session using a visual analog scale. The groups demonstrated similar mental fatigue after practice. Our results suggest that using social media on smartphones during rest periods within a distributed practice impairs performance but not motor learning.