Play therapy receives an innovative, theoretical underpinning for in-depth intervention with children. It is suggested that a new instrument to measure a child's play activity would enhance the understanding of young patients. Interestingly, the word cluster is employed here also to describe categories and components in a child's play. Long clinical experience has shown that nonverbal communication while playing presents its own formal structure, inadvertently adding to the communicative value of any given play situation in therapy. It is possible to pick up intuitively such rich material. But it enriches and makes more plausible treatment efficacy when play activity is measured by the Children's Play Therapy Instrument. The instrument (CPTI), consists of specific, descriptive, structural, and functional scales that can be applied to child patients' play behavior in order to uncover underlying meaning.