A healthy breakfast each and every day is important for students' motivation and achievement.

Breakfast is often cited as the most important meal of the day and vital for students' academic functioning at school. Although much research has linked students' breakfast consumption to better achievement, there has been debate about why and how breakfast has academic benefits. The present study of 648 Australian high school students investigated (a) the role of breakfast consumption and breakfast quality in students' self-reported motivation and their achievement in a science test, (b) the role of motivation in mediating the link between breakfast consumption and quality and students' achievement, and (c) the extent to which breakfast consumption effects are moderated by the quality of breakfast (e.g., more vegetables, fruit, dairy/protein, wholegrains, cereals, water; less sugary drinks, processed meat, fast take-away, unhealthy snack foods). Findings indicated that beyond the effects of personal, home, and classroom factors, breakfast consumption predicted higher adaptive motivation (p < .05), breakfast quality predicted lower maladaptive motivation (p < .05), and in turn, students' adaptive (positively, p < .01) and maladaptive (negatively, p < .01) motivation predicted their achievement. Moreover, adaptive motivation significantly mediated the relationship between breakfast consumption and achievement (p < .05). The effect of breakfast consumption was moderated by the quality of breakfast such that consuming a high-quality breakfast in the morning was associated with the highest levels of adaptive motivation (p < .01) and achievement (p < .05) later in the day. Findings have implications for educational practice and policy seeking to promote a healthy start to the school day to optimize students' motivation and achievement.