The article considers the main provisions describing the features of the introduction and implementation of the elective course on stochasticity for high school students of secondary schools. The stochastic line of the school mathematics course for 10-11 grades is aimed at identifying general patterns, assessing the probabilistic nature of real-world dependences, defining phenomena of random nature, processing statistical data, constructing distributions of random variables, using the law of large numbers and probabilistic sampling method of measurement. The expediency of developing this elective course is due to the importance of knowledge of probability theory for both completing the Unified State Exam in Mathematics and preparing for university studies. The article argues that students who have mastered the methods of measuring and evaluating the phenomena associated with the concept of chance achieve high individual results. As part of the elective course and working in the digital environment, students learn how to use probabilistic and statistical methods to solve problems effectively, the focus of which is conditioned by the establishment of interdisciplinary links with biology, physics, chemistry, astronomy, etc. (for example, the study of Mendel's laws of heredity, Brownian motion (random motion of physical particles), Gibbs' rule, etc.). Skills and abilities obtained help students better understand variability and uncertainty inherent in social and natural processes, transfer their knowledge to new conditions and to new tasks, accumulate personal worldview experience. Thanks to this, high school students have a positive attitude towards a chance and its manifestations, perceive the surrounding reality more objectively. According to the results of the elective course implementation pupils have stable cognitive motives for the cognition of the stochastic component in the environment, deep subject knowledge, which conditions the development of motivational, value, cognitive and activity constructs of stochastic world-view.