Dawn Said:

what are some good 3rd grade science fair project topics?

We Answered:

There is the classic "volcano" or making a light bulb light up by using a potato as a conductor of electricity (there are lots of how to websites on this sort of thing.)

You should find out what kinds of science he is interested in, for example, if he really likes animals he could observe animals at the zoo (and write about what he saw). If he likes rockets/airplanes, he could build his own. If he likes biology, he could look at microorganisms under a microscope and draw them. good luck!