A unique psychometric device, The "Lock Box," has been developed to measure the ability of preschool children to structure a novel problematic situation. The primary purpose of the box is to identify those preschoolers with mental ages ranging from 2 1/2 to 6 years who have difficulty imposing an orderly plan on their explorations and whose movements are random, repetitive, and without apparent goal direction. The box can also be used to identify children with perceptual-motor dysfunctions. Differing from most traditional tests which focus on the product of learning, this device emphasizes the process of learning, is language-free, and utilizes three-dimensional, highly appealing, and lifelike materials. As its name suggests, the box is a large container. Each of 10 compartments within the box contains a different toy and can be closed with a different lock. In administering the measure, the examiner codes the spontaneous moves of the child for 6 1/2 minutes. Five major scores are derived from the performance: total adaptive moves, total non-adaptive moves, number of latches unlocked, organization of moves, and aimless actions. (Rules for administering, coding, and scoring the measure and for constructing age-referenced profiles are indicated). (RH)