Welcome Candi! Thanx Old Coot! That's my prognosis as well. I think it is resultant of the choice, or amounts of the leavening agent. See Alton Brown (food network) on cookies, Candi for further elaboration. Or maybe, the Bakers on this site will certainly be more knowledgeable than I! Hope I helped at least a bit! Atomic Jed said!
Candi: do you mean that the cookies spread out too thin while baking? Then you probably do not have enough flour in the recipe. Sometimes you have to adjust the amount of flour depending on humidity, altitude, etc. And remember to sift, measure and then sift your flour again.
Candi: I had a sheet of chocolate chip cookies that baked REALLY flat so before I baked the second sheet, I added 1/4 cup of flour to the rest of the dough. The second sheet of cookies came out perfect.
Well, from my own experience, I baked a batch of chocolate chip cookies using butter instead of shortening and they came out really flat. When I made the exact same recipe again only using shortening instead of butter they came out perfect.