Executive function is the set of cognitive skills needed for goal directed behavior and is a strong predictor of academic success (Best, 2014). The present study examines the effectiveness of a custom video game designed to train the executive function skill of shifting--being able to efficiently shift attention from 1 task to another. In Experiment 1, students who played Alien Game for 4 hr, mostly at home, improved shifting skill more than those who played a word-search control game (d = 0.40). In Experiment 2, students who played All You Can ET (an updated version of Alien Game) for 2 hr improved shifting skill more than those who played a word-search control game (d = 0.36), regardless of whether the aliens were designed to portray hot or cool emotions. In addition, playing All You Can ET, which targets shifting skill, did not cause an improvement on inhibition skill, which represents a different kind of executive function. These results extend previous findings (Parong et al., 2017), and highlight a somewhat rare case in which playing a focused computer game for a short duration causes improvements in a targeted executive function skill. Overall, the results support the theory of specific transfer of general skills, which suggests that game-based training of cognitive skills should focus on concentrated practice on a target skill to train the target skill rather than divided practice across multiple different skills in an attempt to improve the mind in general.