I've had my yearling since birth and what everyone has posted is true, especially about being naughty sometimes. I also agree with short lessons. I've worked a lot with Luna who pretty much has the demeanor of a golden retriever, but she still likes to test me to see what she can get away with.
I've gotten her to walk over tarps and through water. In my opinion, the best thing to do with them at this age is pony them from another horse. I started out just taking her around our circle drive and can now go short distances down our quiet dirt road.
Stella - sweet, timid, elegant, lovely, lively, amazing
Luna - large, unattractive, naughty, adored