This study examined the relationship between the degree of balance in bilinguals (i.e., degree to which an individual shows equivalence in their level of mastery of two languages) and performance on executive function tests. Twenty-four "more balanced" and 16 "less balanced" Spanish-English bilingual, third- and fourth-grade children completed the Wechsler Abbreviated Scale of Intelligence, the English and Spanish Bilingual Verbal Ability Test (BVAT) (an objective measure of English and Spanish language proficiency), and executive function tests (Wisconsin Card Sorting Test [WCST] and Stroop Test). Significant correlations were found between the degree of balance and error scores on the WCST, such that participants with more similar scores on both English and Spanish BVAT (i.e., the more-balanced group) scored lower on perseveration measures of the WCST than the less-balanced group. Between-group comparisons showed significantly fewer perseverative errors and perseverative responses on the WCST in the more-balanced group compared with the less-balanced group. Stroop Test scores did not reveal group differences. These findings support previous results documenting a "bilingual advantage" on executive function tests and provide support for the hypothesis that the degree of balance moderates the relationship between bilingualism and executive functions.