In this research, the students' achievements in learning Calculus, before and during COVID-19 crisis, are analyzed and compared. Two groups of students, the experimental and the control one, were monitored. Both groups worked in three corresponding subgroups (traditional, hybrid and online) in the frame of different learning environment. The distance learning was applied with the students in the experimental group, in autumn 2020, during COVID-19 crisis, while the control group students learned in autumn 2019, before COVID-19 crisis. The new teaching material was prepared for the students in the experimental group. The comparison between these two groups and their subgroups is described in this paper. It turned out that the students from the experimental group, who used new teaching material for distance learning, had better results than the students in the control group.