We would do a Baby Green division once or twice to make sure the horse was comfortable and confident with the whole concept. Then we do the PreGreen Division with a pro rider on board. I've had a 6 year old ready for the First Year Green division, but that's the youngest. My current PreGreen horse needed a 3' year and a 3'3" year. He'll be a 7 year old First Year horse. We added amateur rides in his 3'3" year and he's done great with it.
I don't see the benefit of a million miles at 2'6" unless the horse has a bad rider. But then, if a young horse has a bad rider, it's unlikely that he'll make up to be a solid 3'6" horse anyway.
Maybe this is off the subject, but I try really hard to discourage my students from doing the "young horse" thing if it's their one and only horse. It just doesn't work well. A green horse needs for their schedule to be determined by the horse's needs- not by the rider's needs or wants.
If you are marketing the horse towards children and amateurs (I imagine to do the children's or adult hunters), what will matter most is that the horse has a show record that shows it's reliable & consistent, and even better if it has good placings/wins under its belt in the divisions you are looking to market the horse toward. If I am looking for an adult hunter, seeing baby green results with a pro is certainly better than no show experience, but it doesn't prove to me that the horse can do what I need it to (cart my butt around 3' even I miss, get nervous, don't give it the perfect ride, etc.).
If your horse is ready to go out there and show at 3' in a polished, confident manner, by all means head straight to the 3' divisions after maybe a show or two at 2'6 to prove he is comfortable. Your horse belongs in a division where it can excel, not where it has to struggle to get down the lines, is nervous about the jumps, or doesn't hold its own against the competition due to inferior quality. If none of those issues apply, go for it!
Nothing more appealing to a buyer than seeing a horse in action doing the job they are looking to do!
My young one did three shows this fall in the baby greens and I rode him in the modified adults at those shows as well. He was more than capable of jumping 3ft and does school at that height at home. But we wanted him to get used to all the sites and goings on that you see at a horse show.
Perfect example- They were dragging the ring next to the one he was showing in. The tractor guy clipped a standard and pulled down the entire jump making quite a lot of noise. My baby spooked and shied to the side but since the jump that was literally a stride in front of him was small it was not much of a problem for him to hop over it. I don't know about you but I would sure rather pop over a speed bump on my baby that is more concerned about what is going outside the ring than have to worry about the jumps as well.
My goals with him were for him to learn the path of going around the course and such. The jumps are never an issue. He literally canters the smaller jumps and does not put much effort into jumping them. I was totally ok with that and knew it would reflect in the ribbons. He could put in a great trip and get second or third to the ones who crack their knees over the little jumps. I plan on moving him up to the Pre-Green's with my trainer this coming season and I will show him in the Adult hunters. My eventual goal is to do the A/O's with him but I really have no timeline as to when we will get there. As JSalem said. He gets to decide what he needs be it more time in the 3' or 3'3" or hooray he only needs limited time and then off to the 3'6" we go!
It totally depends on the horse. Some need time in the 2'6" ring, some don't. Mine was very spooky as a young horse and likely would have scared herself a little at 3' because she jumped so high and hard. She did a full year in the 2'6" & 2'9" divisions (4 y/o), whether that was baby green, young hunters, 3, 4, 5 y/o, etc. depended on the show, & has done the two full pre-green years (5-6 y/o). I showed her in both her 5 y/o & 6 y/o years in the 2'6" and eventually 3' adults. She will probably be an 8 year old first year horse, because not sure I am ready to show her enough for it to be fair to ask her to do the 3'6" until year after next.
You have to go at the pace that makes sense for your horse, but there's no need to linger in the 2'6" divisions if it's not warranted.