I don't now if it was 3" off or not. It seems like it was a little closer for us, but the same thing happened to us last Feb (2012) when we took our 3 1/2 y/o grandson down there. I called my son the night before we left and had him measure my GS in his bare feet. He marked a 40" spot on the wall, then had my GS stand up straight and put a ruler flat on his head and he marked that. My GS was just a tad over the 40" mark, so we knew most of the rides would be very close and that he'd probably be measured at all of them. My D-I-L walked in while my son was measuring him, picked up the phone, and told me it shouldn't be a problem as he'd measured 40 1/2" the week before at the pediatrician's. I told her I just wanted to make sure. Our first night there was at MK (when they were having EMH). He rode Splash Mountain twice with no problem (again this was late at night when you are supposed to be shorter). Big Thunder Mountain was down, so we went over to Tomorrow Land, where he was told he was too short. We didn't want to argue in front of him, but did quietly tell the CM that he had just gotten off Splash Mountain and he could see how wet we were, so knew we were telling the truth. He said the other CM must not have measured him correctly and sure enough he was apparently right, as my GS was measured too short at every 40" ride we tried the rest of the week (including a repeat visit to Splash Mountain that he had ridden just two nights before). He was really trying though, standing as straight as he could and trying to bump his head against the stick. He definitely was not ducking down to avoid that stick, like I've seen some kids do. He was really trying to stretch to hit it.

After the third night, we made our nightly call home, so my GS could talk his parents, and during the phone call he mentioned that he was too short for some of the rides. My D-I-L got me on the phone to ask why and when I told her he was measuring just a tad under the 40" minimum, she said that did not make sense, because she took him to the pediatrician just a week before we left and he measured like 40 1/2" then, plus my son had measured him not just once, but twice to make sure he was accurate the night before we left. We had warned him on the flight down though that he might not be quite tall enough according to Disney's measurements and if he didn't it wouldn't be a big deal as there were lots more there for him to enjoy, so thankfully he was prepared for it to go either way and handled it well. It became a game to him, running up to every measuring thingy, just to see if he might be tall enough.