This study evaluates an automated tool for quantifying plate waste in primary school canteens, aiming to provide a more precise understanding of food waste. The tool, a "plate waste tracker," uses weighing scales connected to a tablet to record food waste and provide feedback to guests. The study analyzed data from 421,015 instances of food wastage across 16 Swedish primary school canteens. The results showed high accuracy, with the tool's plate waste detection within ±10% of manual recordings. However, the tool estimated 40% fewer individual guests compared to manual entries, leading to a 35% higher waste-to-guest ratio. The findings revealed that a minority of students (20%) accounted for a majority (60%) of plate waste, emphasizing the importance of targeted interventions for high-profile wasters. Halving the waste generated by this group would reduce overall plate waste by 31%, highlighting the potential impact of tailored interventions. The study also discussed the limitations and potential improvements of the automated tool, suggesting that it can complement manual methods and contribute to a more sustainable food system.This study evaluates an automated tool for quantifying plate waste in primary school canteens, aiming to provide a more precise understanding of food waste. The tool, a "plate waste tracker," uses weighing scales connected to a tablet to record food waste and provide feedback to guests. The study analyzed data from 421,015 instances of food wastage across 16 Swedish primary school canteens. The results showed high accuracy, with the tool's plate waste detection within ±10% of manual recordings. However, the tool estimated 40% fewer individual guests compared to manual entries, leading to a 35% higher waste-to-guest ratio. The findings revealed that a minority of students (20%) accounted for a majority (60%) of plate waste, emphasizing the importance of targeted interventions for high-profile wasters. Halving the waste generated by this group would reduce overall plate waste by 31%, highlighting the potential impact of tailored interventions. The study also discussed the limitations and potential improvements of the automated tool, suggesting that it can complement manual methods and contribute to a more sustainable food system.