Preschool and Early Grades

Bedtime Math
Great for kids who need some daily math practice but dislike drills. Parents and kids can explore a real-world math problem together, and the different levels let kids of different ages participate.

Prodigy Math Game
An engaging combination of fantasy-based video game and math practice, this adventure also escapes dull drills. It's available as a website and an app.

Bookopolis
Like a Goodreads for kids, this site lets kids log their reading, rate books, and earn rewards for reading. It's great for reluctant readers who might trust another kid's endorsement about a book.

Older Elementary School

Factmonster
Kids can use this as a resource for a variety of subjects. With biographies, an atlas, and other reference materials, Factmonster is an informative place for kids to find fun facts and play educational games.

Free Rice
While very simple, this game has two purposes: to teach words and to feed people. For each multiple-choice vocabulary question answered correctly, 10 grains of rice go to the UN World Food Program.

BJ Pinchbeck's Homework Helper
Provides research and general knowledge in lots of subject areas. Unlike more targeted sites, this one offers links to a wide variety of topics, including history, science, and grammar.