International recognition of the early years as a crucial foundational period has led to the design and implementation of quality rating and improvement systems (QRIS) that define, communicate, and monitor the components of quality in early childhood education and care (ECEC). The aim of these policies is to achieve effective quality assurance and improvement through a system-oriented approach to assessment and evaluation. Informed by ecological systems theory, this paper outlines a three-phase, mixed-methods design for researching a national sample of child care centres that showed overall improvement on the Australian National Quality Standard (NQS) assessment and rating (A&R) criteria. The study samples are drawn from a national dataset of centre-based child care services with two or more A&R rounds and an initial rating of Working Towards NQS (N = 1,935). The results of this study will provide insights into the macro-, exo-, meso- and micro-systems level factors and strategies that support quality in ECEC services.