In this paper, we present the analysis of the students' achievements in learning calculus in a dynamic software environment during the COVID-19 crisis. Two groups of students, the experimental and the control one, were monitored. Blended learning was applied to the students in the experimental group, with the help of "Microsoft Teams" and dynamic software "GeoGebra," in autumn 2020. All students in the control group learned in the classroom without using "GeoGebra" in 2019. The comparison between these two groups of first-year students, regarding their calculus test results, is described in this paper. It is interesting that the results of the experimental group were significantly better than the results of students in the control group, despite the fact that the students from the experimental group learned during the COVID-19 crisis.