In my experience, they've been quite accurate. My youngest had just hit 48" on our measuring wall at home and barely scraped the post at Disney for Rock-N-Roller Coaster. When he was 4 and right at 44", he was too short with his Crocs on but made it with his sneakers the next day. I had told him before we left it would be close and he'd have to stand up nice and tall, and he did.
Thank you! That is helpful.
He'll probably be wearing his sneakers, though I suppose his sport sandals could get some use, too.
Sounds like the measuring sticks at the park account for a normal shoe sole. I measure him barefoot at home (as does the pediatrician).