An analysis of one theory of the acquisition of head movement by children is presented, using longitudinal data from the Mayan language, K'iche'. This theory assumes that children would just require positive evidence of head movement in the input language to instantiate the constructions of their own grammar. The Incorporation Theory addresses the incorporation of a phrasal head into a phrase headed by a different element. The principles and conditions of the incorporation theory are outlined, and the theory's treatment of passives, antipassives, and causatives is sketched, with examples for K'iche'. Data on the ages, numbers of utterances, and utterance length of K'iche' examples are presented. Passive, antipassive, and causative construction in K'iche' children's language samples, are presented and analyzed in the context of the theory. It is concluded that the data offer substantial support for a wide range of predictions. (MSE)