DD 3.5 years was 39" when we went 2 weeks ago. She made it on Splash Mountain without a problem, I think the height requirement line measures a little on the short side. She did not measure at the same 40" requirement line at the other mountains, not on test track either, although after riding it I would not have put her on it. Not enough restraint. My DH also bought her little platform sneakers, which built her up approx. 1". She is a daredevil and wanted to ride all the rides big brother did, who's 7. We used baby swap very successfully, and used cell phones to keep in touch while DH and son were off on space mountain, we were getting princess autographs in Toontown. The cellphones were a godsend for our family, which split up a couple of times during the day to let big kid ride and little kid get her thrills elsewhere. If you want to try and "push the envelope" and get an "almost tall enough" child on, try carrying them into the line. Also, the fastpass line seemed to move very quickly and we carried her on the splash mountain w/o a problem. They did ask if she was measured at the entrance of the line when we got to the actual ride. Good luck!