Using multiple years of data collected from about 100 child care centers in Palm Beach County, Florida, the authors studied whether the Quality Improvement System (QIS) made a significant impact on quality of child care centers. Based on a pre- and postresearch design spanning a period of 13 months, QIS appeared to be effective in improving quality of child care centers. The effects of QIS were quite limited during the first few years, but improvement accelerated over time. Results clearly demonstrated that (1) systematic initiatives like QIS can become efficient and effective in improving quality of early childhood care and education; (2) improvement is more difficult in certain areas of early childhood care and education (e.g., program structure) than others (e.g., activities that centers offer to children); and (3) education change (improvement) takes time. (Contains 6 tables and 5 notes.)