CK-12 Foundation
CK-12 Middle School Math Concepts - Grade 6
Twelve chapters cover a multitude of math concepts found in the Common Core standards for sixth grade. Each title provides a brief explanation of what you will find inside the chapter—concepts from which you can click on and learn more...
Quia
Quia: Capitalization
Here's a nice 10-question multiple choice quiz on scientific notation. Test your skills on scientific notation.