This study aimed to examine the reliability and validity of a diagnostic instrument to be used to measure the developmental level of very young children (aged birth through 36 months) and to screen young children at risk. The subjects of this study were 861 young children. Data were analyzed by item response distribution, item discrimination, reliability, and validity of the scale. Items reflected the developmental level of each age group. Overall internal consistency was relatively high (Cronbach's a=.90~.95), and test-retest (after 2 weeks) reliability was high. Content validity was examined by a panel of experts in the related field. The construct validity as well as the concurrent validity of this instrument was also established.