According to the attentional resources account, mind wandering (or “task-unrelated thought”) is thought to compete with a focal task for attentional resources. Here, we tested two key predictions of this account: First, that mind wandering should not interfere with performance on a task that does not require attentional resources; second, that as task requirements become automatized, performance should improve and depth of mind wandering should increase. Here, we used a serial reaction time task with implicit- and explicit-learning groups to test (...) these predictions. Providing novel evidence for the attentional resource account’s first prediction, results indicated that depth of mind wandering was negatively associated with learning in the explicit, but not the implicit, group, indicating that mind wandering is associated with impaired explicit, but not implicit, learning. Corroborating the attention resource account’s second prediction, we also found that, overall, performance improved while at the same time depth of mind wandering increased. From an implicit learning perspective, these results are consistent with the claim that explicit learning is impaired under attentional load, but implicit learning is not. (shrink)