The article deals with diagnostic assessment conducted in the Finnish language and literature course for classroom teacher students. The research context was a hybrid learning environment, where the students evaluated both their linguistic and pedagogical competence using a self-assessment tool. The research questions were 1) what kind of linguistic competence the students showed in the beginning of the course, 2) how the results of linguistic competence and self-assessment were related, and 3) how the final grade of Finnish language and literature and the matriculation examination test of Finnish predicted the results of a diagnostic test. The data of the pilot research consisted of the results of a diagnostic test of 127 students and their self-assessment based on a five-step criterion-referenced scale. The research was quantitative and statistical methods were used in the analysis. The results showed that there were statistically reliable connections between the results of the self-assessment and the diagnostic test. With the help of the test, it is possible to assess different areas of students’ linguistic competence to some extent reliably.