Abstract: Background and Objective: Adolescent malnutrition will determine a person’s nutritional status in adulthood. Factors that determine whether a person will develop obesity or malnutrition will persist well into adulthood. Breakfast is a full meal that is consumed in the morning. It is recommended to consume meals that are low in fat content and have a sufficient amount of carbohydrates and protein. This study aimed to evaluate the impact of consuming a full breakfast for 6 days on the nutritional status and knowledge of breakfast among junior high school students. Materials and Methods: We recruited a total of 68 students from the 7th, 8th and 9th grades at Al Washliyah 42 Junior High School in Berastagi, North Sumatera, Indonesia. These students were given breakfast for 6 days in a row with counselling on the importance of breakfast via the “Breakfast Ambassador” programme. Breakfast was served by the school catering service and supervised by five ambassadors. Participants were asked to complete a questionnaire before and after the study. Nutritional status and knowledge of breakfast and a balanced diet were also assessed. Results: Approximately 63.2% of students had good nutritional status. The students’ knowledge of breakfast prior to the start of the study was considered sufficient (20.3%). We found an association between the knowledge on the importance of breakfast and breakfast habits but no association was observed between nutritional status and having breakfast. Conclusion: Breakfast habits are not associated with nutritional status. Knowledge of the importance of breakfast is associated with breakfast habits.