K.M.
If he has toys and books in bed with him like ours does, this is what we do. I'd go in and tell her it was time to lay quiet and still in bed (words she understands more then "go to sleep") and if she couldn't do that, I'd have to take away a book or toy from her bed. She does have a lovey and I would NEVER take that away because I know how much it means to her, but she also has at least 2 or 3 books in bed, plus other toys sometimes, and those are all fair game. I've only had to follow through the first time.
I just read that he cries when you leave him at the gate, so this may not work for you, but I though I'd share it anyhow in case you wanted to try it. Maybe trying it for the first time at nap time would work better - he'd understand the consequences without missing out on lots of sleep.