Technically Scooter should be slightly taller than Kermit, but in much of the poser head-to-toe images (some from Muppet Magazine) Scooter appears 3/4 of a head taller than Kermit. Gonzo's technically supposed to be shorter as well, but I think he's grown through the years. Muppet heights are always a debate because there have been many inconsistencies.
Jim Henson didn't keep as many records of the characters as other companies might have when it came to height proportions - probably because they generally didn't have legs 99.9% of the time. Many of the size charts I have seen are of cartoon representations for graphic and lower-end product types. Not bad, just different.
So, Scooter should be taller than Kermit, but shorter than Animal - likely a tad under Animal height when the fella's in his more natural crouched position.