Ecological case study methods were used in four early childhood special education (ECSE) screening programs to identify factors influencing outcomes of screening. Observations, interviews, file searches, and parent surveys were used to obtain multidimensional descriptions of ECSE programs, including outreach, screening, and referral practices. Two outcomes of screening were used as benchmarks for comparing programs: the percentage of eligible preschoolers screened (participation rate); and the percentage of screened children referred for further developmental assessment (referral rate). Results indicated that screening and referral practices varied considerably among programs, although few practices consistently influenced screening outcomes. Participation rates were clearly related to school district size and the accessibility of screening to the public. Referral rates were most obviously influenced by screening purposes, second-level referral decisions, separate speech/language referral criteria, and subjective judgment. Relationships among community agencies influenced both participation and referral rates. Considerations and guidelines are presented for evaluation and improvement of ECSE screening programs. (Author)