This is a tough age to find a manageable and original project for. Why not produce your own index of web sites that have astronomical information of use to 7th grade students? This is not really a 'science' project, but it would be invaluable to your science teachers, and to me!
How about correlating the annual sunspot numbers against the number of aurora seen in canada and alaska? Visit the NASA MIDEX/IMAGE site and look under Activities page for more related ideas.