Maternal interpretations of the intentionality of infant behaviour have played a key role in many theoretical accounts of the development of intentionality. However, the assessment of maternal interpretations has generally proceeded in an indirect fashion. The present study sought to assess maternal interpretations in a more direct manner. Sixty primiparous mothers of 4‐ or 8‐month‐old infants viewed video clips of unfamiliar infants engaged in social‐, object‐ or non‐directed activities and rated the actions for perceived intentionality. Results indicated that mothers of younger infants assigned more intentionality to social behaviours than did mothers of older infants, suggesting that maternal interpretations change over the course of infant development. Explanations for this pattern are explored, including the possibility that mothers become less sensitive to established behaviours or that they use a type of moving threshold to judge infant actions. Future avenues of research are suggested.