You might think vinegar and baking soda are old hat, but--believe it or not--most middle school students have only been cursorily introduced to them. Don't forget that kids think they know everything. ;)
This activity gives students a chance to work with something they are familiar with (vinegar and baking soda) and apply it to something they are less familiar with (scientific method concepts and vocabulary). It takes them through each step and includes a wrap-up at the end.
The project moves more smoothly and quickly in groups.