Big Boy Bed

We have been trying to get Luke to sleep in a twin bed this week. So far that is not going well. The longest we has made it is 3 hours one night. He just doesn't seem to understand that he is suppose to stay put. Dominic was totally different - we put him in the bed, told him to stay there and he did. No such luck with Luke. After 45-60 mins of putting him back in bed, he ends up in the crib the rest of the night. I think this is going to be a long process.