In an effort to bring rigorous research into the education and social sciences field, the past decade had seen an increase in the advocacy of randomized controlled trials. The argument in favor of using randomized controlled trial is that one can evaluate the impact of an intervention in comparison to a control group with confidence during a summative evaluation. However, before coming to the stage of conducting a randomized controlled trial, extensive effort in planning and conducting process evaluation is needed. This article examines the perspective of an early childhood evaluation in the United States, and particularly highlights the challenges that arise when a state's whole system is being evaluated, where the system consists of a variety of program models and the provision of early childhood services is universal in the system. The challenges are highlighted so that future evaluators will be aware of such issues in planning their universal systemwide evaluation.