Abstract
Prospective research shows that substance users in an urban school population may have greater than average problems associated with mobility, reading skills, absenteeism, dropout, retention in grade, and school cooperation. Methods are described that were used in a 4-year longitudinal study beginning in the 4th and 5th grades of 111 District of Columbia public schools. The methods helped meet needs for accurate tracking, accurate data collection, protection of confidentiality, and acquisition and maintenance of the population.