Adolescence, as a period of many changes and stressful events, carries a risk of developing internalizing symptoms, especially depression and anxiety, and studies confirm that girls are almost twice as vulnerable when it comes to developing these symptoms. Numerous studies have linked the ability to recognize one's own affective experiences, such as emotions, moods and rich emotional vocabulary, to an individual's well-being and mental health. Some researcherssuggest that one of the factors that prevents the development of internalizing symptoms after stressful experiences could be precisely emotion differentiation. The mentioned construct is defined as the ability to recognize and accurately mark emotional states, providing more precise information about the situation and facilitating the regulation of emotions. Given the above, the present study aimed to investigate the psychometric characteristics of the measure of emotion differentiation, to determine whether boys and girls differ in emotion differentiation, stressful life events and internalizing symptoms, and to investigate the relationships between these constructs. The study included seventh and eighth grade elementary school students: 133 boys and 132 girls, using the Emotion Differentiation Test, the Emotion Vocabulary Test, the Stressful Life Events Scale for Children, and the Depression, Anxiety, and Stress Scale. Exploratory factor analysis determined the one-factor structure of the measure of emotion differentiation andit was determined that it has satisfactory psychometric characteristics. The analysis of the data showed that girls performed better on measures of emotion differentiation and emotional vocabulary, experienced more stressful events in the last 6 months and more stressful events related to COVID-19, and had more internalizing symptoms than boys. Furthermore, at the group level, there was a negative low correlation between emotion differentiation and the number of stressful events in the last 6 months and a positive low correlation between emotion differentiation and assessments on the scale of anxiety COVID-19.