Background: The ability to understand and manage emotional experience is critical to children's health. This study confirmed the validity of the How I Feel (HIF) Questionnaire, a measure of children's emotional arousal and regulation, exploring its associations with measures of emotional and social functioning. Methods: The sample was comprised of 1379 Italian students (aged 8 to 12 years) who attended schools interested in the study aims. Participants completed the 30-item HIF scale, and measures of emotional self-efficacy and social desirability (SD). Factor structures were assessed using confirmatory factor analysis. Invariance by age and gender, internal consistency, temporal stability, and concurrent validity were also tested. Results: A 3-factor model was identified: frequency and intensity of (1) positive emotion--PE (8 items, a = 0.82), (2) negative emotion--NE (12 items, a = 0.86), and (3) positive and negative emotion control--EC (10 items, a = 0.77). This factor structure was invariant across age and gender groups. The HIF displayed moderate longitudinal stability over a 15-month period and a low social desirability effect. Positive emotion was positively associated with social acceptance and visibility, and negatively with social withdrawal. Conclusions: The HIF is a reliable and valid measure for research and school intervention promoting students' emotional and mental health.