Food waste is a problem that needs to be addressed to achieve sustainable development. There is a need for interventions that can reduce food waste, including in organisations already aware of the food waste problem. Swedish school canteens have experience of food waste reduction, but need tools to achieve further reductions. This study tested four interventions (tasting spoons, awareness campaign, a plate waste tracker and a guest forecasting tool) designed to reduce food waste in school canteens. Each intervention was introduced in two school canteens, while seven school canteens acted as a reference group. The interventions were compared with baseline food waste before the intervention and with the reference group. All interventions reduced total food waste (by 6 to 44 g/guest) compared with the baseline, but the reference group also reduced its food waste. The awareness campaign reduced plate waste most, by 13 g per portion, which was 6 g/portion more than the plate waste reduction in the reference group. The forecasting and plate waste tracker interventions reduced serving waste most, by 34 and 38 g/portion, compared with 11 g/portion in the reference group. Some interventions also had an effect on waste fractions they were not designed to target, affecting the total waste by shifting the waste. Interventions should always be seen in a context and be implemented in combinations that increase overall sustainability. Thus forecasting is an effective way to reduce serving waste, plate waste tracker and awareness campaign are effective tools to reduce plate waste in school canteens.