Demonstrate to your middle school science learners how chalk breaks down in a weak acid. Discuss what affects acidic rain might have on ecosystems. Lab groups then choose one of two questions: "How does acid precipitation affect an aquatic ecosystem?" or "How does acid precipitation affect terrestrial ecosystems?" They work together to design and perform an experiment to answer their question. This is a stellar lesson on acid rain, and it reinforces practice of lab skills and the scientific process.