Dog trainers make widespread claims that training dogs to improve self-control is essential to solving behavior problems in domesticated dogs. We investigated whether one aspect of self-control, motor inhibition, covaries in dogs with varying levels and contexts of formal training. We tested pet dogs with little formal training and dogs with high levels of training who compete in scent work, barn hunt, and agility. All dogs were tested for motor inhibition on the cylinder task, a validated self-control task. First, in familiarization trials, dogs watched a piece of food placed inside an opaque cylinder and were subsequently allowed to retrieve it. Then, in test trials, dogs watched a piece of food placed inside a transparent cylinder. This transparent variation of the task requires dogs to inhibit the response to directly approach the now-visible food and instead detour to an open side. In contrast to the belief that highly trained dogs would uniformly demonstrate better self-control, trained dogs did not perform better than untrained dogs. In fact, dogs who competed in barn hunt performed significantly worse compared to untrained pet dogs. These findings suggest that self-control may involve a complex set of mental processes that do not uniformly generalize to multiple contexts.