Ecological case study methods were used in an exploratory investigation of four early childhood special education (ECSE) screening programs. Possible influences on screening outcomes were identified. The screening outcomes selected for comparing ECSE programs included (a) the percentage of eligible preschoolers screened (participation rate) and (b) the percentage of screened children referred for further developmental assessment (referral rate). Observations, interviews, file searches, and parent surveys were used to obtain multidimensional descriptions of outreach, screening, and referral practices. Results suggested that few screening and referral practices influenced screening outcomes in a consistent manner. Participation rates were related to school district size and the accessibility of screening to the public. Referral rates appeared to be influenced by screening purposes, second-level referral decisions, and subjective judgment. Relationships among community agencies appeared to influence both participation and referral rates. Policy considerations and directions for research are discussed.