I think it all depends on what he was previously doing, if he was sleeping in the same bed as you or the same room it will be a bigger adjustment than if he is just moving from a crib.Make a big deal out of his big boy bed, and show him how neat it is to have his own bed, that can be decorated with his favorite things. When I moved my daughter over, I told her how excited she should be, and then took her to the store and gave her an option of a few bed sets that I thought she would like. Letting him choose his bedding will make it feel even more special, and it is one more thing that "big boys" can do that babies can't.If he has been co-sleeping, start things out a little slow to let him adjust to the new rules. Cleary say "This is where you are going to sleep now, I will be right in the next room." I would sit with him for a day or two until he falls asleep and after that read a story or what ever your normal routine is and then walk out.If he gets out of bed the first time tell him it's time to sleep now, and take him back to bed. If he continues to get out of bed with out saying anything take him back to bed and walk out. It might take a few hours but he will eventually get the idea that you are not going to let him out of his bed.I also like to put a couple books and my daughters favorite stuffed animal to cuddle up with. She typically flips through the book and plays with her minnie mouse in her bed until she falls asleep. As long as you stay firm and encouraging he will be sleeping in his own bed in no time.