This study aimed to evaluate the effect of a nutritional intervention involving a problem-raising approach and the use of pictorial representations on the promotion of knowledge and practices of healthy eating among adolescents. This randomized study included 461 adolescents from public schools in Brasilia, Federal District, Brazil (intervention group: 273 students from four schools; control group: 188 students from three schools). Mean age was 14.8±1.0, and 52.9% were boys. The intervention consisted of three meetings with interactive activities about principles of healthy eating, food classification, importance of reading labels and analyzing food advertising critically, and representations of healthy and unhealthy meals and their sugar, salt, and fat content. Pictorial materials consisted of food drawings, food models, and a food packaging model. Controls were not exposed to any activity. Dietary knowledge, consumption, and behaviors were the variables of interest. The intervention group showed a higher mean score of correct answers to questions about dietary knowledge than the control group (p = 0.0006), with higher odds of correctly answering questions about in natura (OR: 3.7; 95% CI: 1.9–6.6), minimally processed (OR: 3.6; 95% CI: 1.9–6.4), processed (OR: 2.2; 95% CI: 1.1–4.3), and ultra-processed foods (OR: 3.5; 95% CI: 1.8–6.6) and composition of ultra-processed foods (OR: 2.4; 95% CI: 1.3–4.4). Participants in the intervention group were also 2.5 times more likely to correctly answer questions about the importance of the dietary environment (95% CI: 1.1–5.5) and caution with food advertising (95% CI: 1.2–5.3) than controls. Increased weekly consumption of vegetables (p = 0.0077; OR: 2.4; 95% CI: 1.26–4.51) and reduced consumption of soft drinks (p = 0.0212; OR: 0.36; 95% CI: 0.15–0.86) were observed in the intervention group compared to the control group. The proposed intervention increased adolescents’ knowledge and improved some of their dietary habits. Educational activities using a problem-raising approach and pictorial representations of food appear to be effective in promoting healthy eating practices among adolescents. [ABSTRACT FROM AUTHOR]