In the Early Childhood Education and Care (ECEC) sector there is a move to reduce oversight costs by reducing the frequency of quality assessments in providers who score highly consistently across time. However, virtually nothing is known about the stability of ECEC quality assessments over time. Using a validated measure of overall classroom quality, we examined stability of quality in a sample of over 1000 classrooms in licensed child care centres in Toronto, Canada over a 3-year period. Multilevel mixed-effects linear regression analyses revealed substantial instability across all types of ECEC centres, although publicly operated centres were somewhat more stable and tended to have higher quality scores. We also found substantial variance between classrooms within ECEC centres. None of the structural, child/family and neighbourhood characteristics we examined were significantly related to stability of quality ratings. The lack of stability found in our sample does not support the use of a risk-based approach to quality oversight in ECEC. Large within centre classroom quality variance suggest that all classrooms within a centre should be assessed individually. Furthermore, classroom level scores should be posted when scores are made public as part of accountability systems. Future research should, in addition to administrative data used in our study, explore how factors such as educator training, participation in program planning, reflective practices and ongoing learning might improve stability of quality over time.