ABSTRACT The study investigated joint action performance and joint unintentional transfer of learning in two cohorts of elementary school children. Thirty‐two first‐graders (mean age 6.6 ± 1.22 years; 22 females; all White) and 32 second‐graders (mean age 7.8 ± 0.27 years; 15 females; all White) performed a Joint Simon task before and after performing a joint spatial compatibility task in which stimulus position was mapped incompatibly to the response position. We assessed whether, prior to training, children displayed a reliable Joint Simon effect (JSE), indicative of co‐representation, and whether age‐related differences emerged in its magnitude. Furthermore, we assessed whether the effect was affected by a jointly performed practice. Both age groups showed a significant JSE that was eliminated by the joint incompatible practice. No significant age‐related differences emerged. Our results indicate that 6‐ to 8‐year‐old children are influenced by the presence of another agent and suggest that the knowledge acquired during joint task performance may automatically and unintentionally transfer to a subsequent similar task.