Your school website is a good website to find a science fair project. Science programs for kids typically have websites with projects listed. PBS has a website for kids that includes science projects.
google.com or science fair projects.com
Decomposition, energy, light, electricity, and photosynthesis are all good science fair topics
A good science fair project for a 6th grade level would maybe be something like the following: Does the average speed of a gymnast affect how their vault score? I'm trying to think of a good 7TH GRADE level gymnastics science fair project. advice?):
tomatoes and cucumbers
There are plenty of great 8th grade science fair projects. You could play with something like air concepts for example.
go to the site Google.com and ask good science fair projects
A good and popular science project is nothing that yo ugly self can do !!
The grade is up to how diligent you are. Below are some sites that have lots of science fair projects.
Volcanos, and why coca cola explodes when you put mints in it
Bread Mold:The Inside Facts
kicking yo in da mouth