This study explored the Junior Brixton Test (JBT), an executive function (EF) measure for children, in comparison to the Wisconsin Card Sorting Test (WCST) in a sample of 6- to 8-year-olds, all attending the first 2 years of elementary school. Factor analyses indicated two main domains in both measures, namely concept formation and cognitive flexibility. However, within the cognitive flexibility domain of the JBT, perseveration scores reflected qualitatively different perseverative errors. More specifically, perseveration of previous rule and same stimulus scores loaded on the same subcomponent, whereas perseveration of same response loaded on another. The latter score was also negatively correlated both with a measure of general reasoning ability and a memory span task. The authors argue that the JBT is a promising tool to explore individual variations behind seemingly one type of executive function error, namely perseveration.