Background. Readiness for professional self-determination of schoolchildren often remains outside both empirical research and career guidance practice, despite the relevance of the topic noted by many career pathologists. With their research, the authors tried to fill the gap in knowledge to a certain extent. Objective. The article aims to highlight the problem of professional self-determination of schoolchildren in grades 8-11 and offer methodological tools for diagnosing the level of readiness. Methods. The data for analysis were obtained as a result of a questionnaire conducted by specialists of the «Human Technologies» Centre within the framework of the AllRussian Professional Diagnostics programme in 2018. The event included career guidance testing of schoolchildren from 47 regions of the Russian Federation. The study involved 20,410 students in grades 8-11. Results. The analysis of the data made it possible to identify and classify the difficulties faced by students in the process of professional self-determination, as well as to identify factors that need to be taken into account in career guidance practice. It was revealed that when assessing the level of readiness of a student for professional self-determination, it is important to take into account not only the degree of their readiness to make a decision, but also the breadth of their horizons, the level of knowledge about the world of professions in general and the educational system in particular. As a result, the article presents a methodology for assessing readiness for professional self-determination, provides evaluation criteria and the structure of significant factors. Practical significance. The methods and testing procedures given in the article can be used in organising career guidance work at school at the stage of assessing students’ readiness for professional self-determination.