First of all I would like to say that I appreciate the discussion we are having. It is always valuable to me to have to justify, or claify my thinking.
I agree with you that many of these things can also be done in a low tech way - sans calculator. In this case the elements of time and tenacity (the possible lack of both) could limit the explorations. Sometimes just the novelty of using a piece of technology will increase students tenacity or "stick-to-it-ivness".
My purpose in discussing them was in reference to Chi-Tien's comment that he could see absolutely no way that calculators could be used in the K-4 classroom that would not be harmful to students learning.
At all times, in every curriculum area, I consistently attempt to utilize any and every means available to "increase the probability" that more students will learn.
>Can fourth graders relate to rational numbers though?
Very definitely, when given appropriate activities and ample time:-)