How does a horse change between weanling and 3 year old?

I chose my coming-4-year-old as a weanling. I know basically nothing about foals but I really liked the way he carried himself. Most foals have good suspension in the trot like Winter said above, but there was something about his shoulder and neck set that I really liked. I had initially been interested in the second colt his breeder had (technically his nephew) but after seeing them both I thought that the one I chose would ultimately be the better mover. My trainer agreed based on the pics and videos I took, so I bought him. A good friend of mine (also trainer’s client) ended up buying the other colt. At 1, they both went to a breed futurity and the other colt scored higher than mine, who was pretty awkward looking. Now that they are both under saddle it is again apparent that mine is the better mover. We’re aiming for the 4-year-old championships this year!

Here are trot pics of him at 5 months and 2 years, in case it helps at all: https://libby2563.shutterfly.com/pictures/110

My advice is: Even though I had an opinion about mine that seems to have proven correct, I would not have felt comfortable choosing a youngster on my own. I think it takes a lot of experience to see potential at that age. Start with known bloodlines and find some whose breeding and look you like. Then can you show the pics and videos to a trainer you trust? Someone with experience raising babies and bringing them up through the levels. My trainer has been around the block…used to breed, has bought plenty of weanlings and yearlings, has started hundreds if not thousands of horses, and has taken more than a few up to GP. I’m lucky to have her guidance!