Common Sense Media shares favorite apps that help kids with homework.
How Stuff Works (Free)
Recommended age: 12 and older
Popular, trusted resource covers mature topics responsibly
Devices: iPhone, iPod Touch, iPad, Andriod, Apps for Windows, Windows Phone
Yup — Homework Help With Math and Chemistry Tutors (Free trial, then subscription-based)
Recommended age: 13 and older
Live tutors help tweens and teens with math and science.
Devices: iPhone, iPod Touch, iPad, Android