This study describes the development of a Learning Event Checklist and a running record of children's behavior to help in assessing and mainstreaming children with disabilities. The sample consisted of 138 children between the ages of 2 and 6 years, mostly males, in special education preschool programs. The running record was designed to assess each child's potential for using the preschool environment for learning, by determining and classifying immediate sources of learning for individual children. Observed learning sources in rank order of frequency were responding to an adult, interaction with objects, social conformity, observation of other children, responding to a child, asking an adult and asking a child. Implications of the project for mainstreaming are discussed. Instructions for use of the Learning Event Checklist are provided, with examples from the running records. (PB)