The COVID-19 pandemic has brought the rapid transition to online quantitative education, leading to unique challenges and opportunities in assessments for both students and instructors. Focusing on undergraduate students and teaching staff at a Canadian university, this study investigates and compares their experiences and perspectives regarding assessment in online mathematics and statistics courses during the pandemic. Framed by the theory of community of inquiry, our analysis highlights how assessment affected the cognitive, social, and teaching aspects of their learning and teaching experiences. The analysis was based on interview data from the focal student and teaching staff participants. Findings indicated that students and teaching staff had complex experiences with the assessments designed and administered in the online courses during the pandemic. Such complexity was attributed to varied factors, such as technology integration, uncertainty during the pandemic, assessment structure, alignment with course content, and connection with real-life applications. Implications for transforming the assessment practices to meet the demands of students and instructors in online mathematics and statistics education were also provided.