Consider your alternatives. If yours is a school that uses disposable lunch trays, consider replacing them with reusable trays. If you do not want to purchase reusable lunch trays, look into the cost for disposable lunch trays that are fashioned out of recyclable materials, such as sugarcane, that are more eco-friendly.
Fix the broken dishwasher or pay for the school to upgrade the kitchen so that it is more conducive for washing reusable dishes and trays. If you replace your disposable trays with those that are reusable, you will require the means to wash them after each use. Make sure the cafeteria kitchen can accommodate this process.
Consider going tray-less for a day. Select a day of the week -- same day every week, to make it easy to remember -- on which students must bring a sack lunch from home. On this day each week, the school cafeteria will not have to use trays because it will not be serving prepared meals to students. In the end, you save money and reduce waste by not having to use disposable trays and you don't have to wash the reusable ones, and you can even give the school cook a day off.
Compare the prices of all of these options. Decide which option is best for your school's budget, as well as for the environment. For instance, if you choose to use reusable trays made from recyclable materials, you might have to hire a dishwasher, which is may not be conducive to your budget. Therefore, a disposable tray made from recyclable materials -- or no trays at all -- might be the more cost-effective decision.
Institute a new rule that students must supply their own lunch tray for meals, or other means for carrying food, such as hand baskets or bags. This gives students and parents the choice of what product they wish to use, while not costing the school money.