Several authors have shown that vegetables a re the most commonly wasted component in school lunches and enhance the importance of food education on topics such as food waste and vegetable consumption. The present research evaluated the efficacy of a single session of food education on vegetables waste and consumption. The data collection was focused on primary school students from a school located in Guarda district (Portugal). A vegetable selective aggregate weighing from the lunch plate was required in two distinct phases: before and after a single 30 min nutritionist’s intervention. The variables collected were the quantities of vegetables produced, leftovers and plate waste. Through these weighings, it was possible to measure the variables: distributed vegetables, consumed vegetables, vegetables waste, leftovers index, plate waste index. The use of materials such as a scale, suitable containers, gown, disposable gloves, cap and office supplies were necessary. In total during the two phases, 870 meals were evaluated. Measures of central tendency and statistical analysis tests were used. At the end of the present research, it was possible to verify significant results in the reduction of the vegetables leftovers index and in the increase in vegetable consumption per capita, through the nutritionist’s intervention. There were significant differences in the reduction of the index of vegetable leftovers and in the increase in the consumption of vegetables per capita and no significant differences in total vegetable waste. Potential causes and strategies for future research were also discussed. This study demonstrates how a nutritionist’s intervention, in a school context, could translate into behavioral change in nutrition and sustainability terms.