I Know That is a kid-friendly site that offers a lot of interactive activities in all academic areas. These games and activities are aimed at improving problem-solving skills, language arts skills, grammar, geography, mathematics, and so on. You can easily navigate by subject or by appropriate grade-level. Visit the website at www.iknowthat.com. (No registration is required to access all games/activities.)
Read.Write.Think offers a collection of online Student Materials to support literacy learning in the K-12 classroom. These interactive tools can be used to supplement a variety of lessons and provide an opportunity for students to use technology while developing their literacy skills. Visit site.
Busy Teacher's Cafe is also another great site for free printable worksheets on academic activities like reading comprehension, language arts, writing, and math. Visit their website at www.busyteacherscafe.com/printables.htm