All Kids Network: Comprehensive, easy-to-download / print worksheets for all subjects.
Jumpstart (K-6) - Math
Math Games, Logic Puzzles and Brain Builders
A Plus Click
Math Score: (paid subscription) - Super intuitive and easy-to-use
Math in French (Elementary)
KIDZ MD: Daily free science or cooking experiments to do at home.
Funology: Cool science experiments for younger children
Science Spot: Science projects and printable worksheets that can be completed with or without Internet access https://sciencespot.net/Pages/classhome.html
The Happy Scientist: Just explore, have fun, and learn some science along the way.
NASA for Kids: Space science for kiddos
Ask Dr. Universe: A science-education project from Washington State University. Kids can send Dr. Universe any question they may have about history, geography, plants, animals, technology, engineering, math, culture, and more.
Cells Alive: Learn all about cells
Steve Spangler’s Science: Tons of science experiments that you can do at home
Weather Wiz Kids: From rainbows to tornadoes and winter storms to tsunamis, meteorologist Crystal Wicker breaks down the fascinating world of weather. http://www.weatherwizkids.com/
Youngzine: News and more for kids