Ideas for a 7th grade science project include using common household materials to make clouds or self-inflating balloons. Interesting projects can be made with very little expense.
Seventh graders typically have a better understanding of scientific subjects, such as chemistry and physics, which will provide a wider variety of options for interesting science fair projects. Commonly used household items like baking soda and vinegar can produce some interesting results, and urban legends — such as the one about Pop Rocks and soda — can also be turned into a fun experiment.
For projects that don't require chemicals or expensive materials, use the Internet to conduct surveys. These surveys can be used to find the answers to questions such as "Does the weather really affect mood?" and "Does color preference change with age?"
Keep in mind that the basic elements of a science fair project include a hypothesis, a procedure for testing and a report of the findings.