The need for a simple method of examining the early postnatal development of mouse models of human neurodevelopmental disorders has become evident. The following method for evaluating the developmental milestones of newborn mice allows for fast throughput of large numbers of mice in a battery of tests that examines weight gain and the reflexes and coordinated movements that are expressed at differing periods throughout the first 21 days of life. Sophisticated equipment is not required, and the measures focus on the day of first appearance of a developmental sign, reflex, or coordinated movement.