Beat the Clock

My kids love these Beat the Clock books from Lakeshore Learning Materials.  I got them with a grant and have one for every student.  For math, I teach a math lesson using my Smartboard, and then the students have some sort of practice and/or assessment afterwards.  Early finishers are allowed to get a Beat the Clock book which have either addition or subtraction facts.  The students start the timer and then solve away.  After they establish the first time, then the challenge is to beat the clock.