The purpose of this study was to investigate the effects of variations in the day care environment on linguistic and social-emotional development of pre-school children in Singapore after home background has been taken into account. This study examined differences in the environment of 16 day care centres. Characteristics of the environment were assessed by the Early Childhood Environment Rating Scale, ECERS (Harms & Clifford, 1980) and the Target Child Method of Observation, TCM (Sylva, Roy & Painter, 1980). The ECERS measured the physical and programmatic features of day care centres and produced a total 'quality' score and seven subscale scores. These consisted of assessments of personal care and routines, furnishing and display, language-reasoning experiences, fine and gross motor activities, creative activities, social development and adult needs provided in day care centres. This rating scale was validated in Singapore and discriminant validity was established. Reliability was also obtained before proceeding with the assessment of the day care environments. The TCM investigated the interactive features of day care centres and consisted of typical activities and social interactions experienced by children. Inter-observer reliability was established and child behaviours were systematically observed and coded for 12,800 thirty-second intervals. Day care effects were investigated by assessing children at two time points. A pre-test,consisting of linguistic and social-emotional assessments, was conducted on 122 pre-school aged children at the beginning of the year and a post-test administered towards the end of the year. Data analysis was conducted by regressing these outcomes on the ECERS measure of the day care environment. T-test analyses were also conducted to investigate differences in typical child behaviours (as nasured by the TCM) between 'high' progress centres and 'low' progress centres. Child characteristics and home background variables were included in the analyses to control for possible confounding of the effects of the day care environment on children's outcomes. This study found that total centre 'quality' and specific subscales on the ECERS were related to some aspects of linguistic and social emotional development of children. Results also suggested that certain child activities and social interaction were associated with higher progress in language development.