COVID-19 had significant impacts on the field of education and, in turn, on school-based research. During this unprecedented time, nearly all schools closed, disrupting learning as schools shifted to a virtual format. Addressing the lasting effects of school closures is a major challenge in the post-pandemic education climate. Educators indicate these challenges have limited their willingness or ability to participate in research. We analyzed over 700 reasons for refusal in four recent education studies to examine the effects of COVID-19 on school-based research. About 4% of education leaders cited COVID-19 as the primary factor impacting their unwillingness to participate, while related factors such as learning loss, instructional time, or teacher shortage were cited approximately 16%. Over 40% of schools declined because of required testing and surveys. Given the voluntary nature of participation, the remaining schools declined for various reasons not necessarily related to COVID-19. Insufficient participation can be detrimental to research by impacting the quantity and quality of data collected and possibly introducing bias into the data, thus skewing findings. In the post-pandemic era, school-based researchers must be mindful of the challenges schools face and develop mitigation strategies to contend with the reluctance to participate in external research.