I actually used this with my gr. 1/2 class, even! We used it after reading the math lit book "Equal Schmequal"... Check out Christine's lesson plan on our District Math Site: http://web.sd71.bc.ca/math/index.php?page=lessons-activities-grade-2
Yes, Alissa the lesson plan that Michelle is referring to is fanatastic and kids of all ages seem to grasp this concept pretty quickly. In fact my 6 year old son intuitively got it before my 10 year old.