School plate waste is of particular concern worldwide due to its adverse impacts not only on resource use and the environment, but also on students’ health, physical maturation, and academic achievement in the long term. Previous studies on school plate waste have all been conducted in industrialized countries, and more studies are badly needed in developing countries. In this paper, we report a pilot study on the patterns and causes of plate waste in school lunch programs in Beijing, China, by a combination of physical weighing, questionnaire survey, and semi-structured interview approaches. Our results show that the average amount of food waste generated by school students in Beijing in 2014 was 130 g/cap/meal, accounting for 21% of total food served. Staple food (43%) and vegetables (42%) were the dominant proportions. Buffet meals resulted in less plate waste than packed meals and set meals. Food supply patterns, the quality of canteen service, and the dietary habit and students’ knowledge of food production were the main influencing factors behind plate waste. To our best knowledge, our pilot study provides a first understanding of the overlooked plate waste in school lunch programs in China, and a good basis for further analysis in this field, and will be helpful in informing policy-making in relevant nutrition and education programs in schools in China.