add and subtract efficiently and accurately with single-digit whole numbers.

http://www.aplusmath.com/Flashcards/addition.html

http://www.aplusmath.com/games/picture/AddPicture.html

http://www.oswego.org/ocsd-web/games/SumSense/sumsub.html

http://www.numbernut.com/basic/activities/sub_quiz_1-v.shtml