When bilinguals speak, both fluent language systems become activated in parallel and exert an influence on speech production. As a consequence of maintaining separation between the two linguistic systems, bilinguals are purported to develop enhanced executive control functioning. Like bilinguals, individuals who speak two dialects must also maintain separation between two linguistic systems, albeit to a lesser degree. Across three tests of executive function, we compared bilingual and bidialectal children's performance to that of a monolingual control group. No evidence for a bidialectal advantage was found. However, in line with a growing number of recent partial and failed replications, we observed a significant bilingual advantage only in one measure in one task. This calls the robustness of the bilingual advantage into question. A comprehensive review of studies investigating advantages of inhibitory control and cognitive flexibility in bilingual children reveals that the bilingual advantage is likely to be both task and sample specific, and the interaction between these factors makes qualification of the effect challenging. These findings highlight the importance of tracking the impact of dual linguistic systems across the lifespan using tasks calibrated for difficulty across different ages. This study provides the first test of a possible bidialectal advantage in childhood, comparing bilingual and bidialectal children’s performance in executive function tasks to the performance of monolingual children. No bidialectal advantage was apparent. Further, the ?established’ bilingual advantage was found only in one measure in one task, calling into question the robustness of the effect.