Experiment I required first, third, and sixth graders to identify the actor or experiencer from active and passive sentences with actional and three subclasses of experiential verbs. Actional passives were understood better than experientials, with no difference among the subcategories of experiential verbs, and no effect of verb frequency or regularity. Response distributions for each verb type did not show two populations of subjects – one knowing and the other not knowing the passive – but approximately unimodal distributions whose mean increased with age. Experiment II studied preschoolers. Again, the actional passives were systematically easier than the experientials, and again, for neither verb type did the response distributions show two distinct subject populations, one competent and the other incompetent. The forms of the distributions cannot be wholly accounted for by fluctuating attention to cues to passivization, but indicate that many children have partial knowledge of the passive (increasing with age). A hypothesis about the nature of this partial knowledge accounts for the gradual acquisition and the difference between the verb types.