The development of a sound methodology is crucial to the success of any research model. In observational research design, several factors must be considered for the data collection phase to be without contamination and yield data that will generate answers to research questions posed. Determining the best positioned observers to obtain the information needed is one of the first questions to be considered in developing the research methodology. Choosing the right instrument to obtain data to answer the research question requires a thorough understanding of the various measures available and should be considered in the context of the decisions related to the primary data collectors. This chapter will explore why (1) child observation should be an intricate part of a teacher's portfolio of best practices; (2) choosing assessments as part of developing the research design is critical to accurately assess success in meeting program goals; (3) it is important to measure contributing factors in classrooms that impact child outcomes, address challenging circumstances that call for observational assessments; and (4) addressing challenges in collecting and using observational data in conducting research in the future is imperative to best analyze the changing landscape . (author abstract)