This research developed an authentic assessment of student online learning in a mathematical classroom during the coronavirus (COVID-19) pandemic based on the conceptual framework of Tall (2020a). The target group comprised five students from Rajamangala University of Technology Suvarnabhumi, Suphanburi Center and seven students from Rajamangala University of Technology Phra Nakhon who enrolled in the Calculus 2 course. Data were collected from an authentic assessment of student online learning in a mathematical classroom using Google meet, structured interviews, assigned tasks and field notes. Findings indicated that students’ thinking progressed from an embodied world into a symbolized world and then into a formalized world through online teaching technology by applying mathematical concepts to promote increased learning output.