The new research results on the online- testing method in the Latvian education system for a learning process assessment are presented. Data mining is a very important field in education because it helps to analyse the data gathered in various researches and to implement the changes in the education system according to the learning methods of students. The aim of the research was to analyze how much time students devote to each task depending on the task type and the cognitive activity level in the online national test. Research methods: 1) analysis of scientific literature; 2) descriptive statistics and dependency analysis for processing the data. Research results showed that the time spent on tasks depends not on the complexity of the task but on the form and formulation of it. [For the full proceedings, see ED619611.]