From what I've read, you usually need to start taming them before they are a day old - and even then not all will become tame. Take them out of the brooder and sit with them in your lap in the evening and such - but as you have noticed it doesn't take many days before they become too scared to sit still long enough to realise you are not killing them, which is why you need to do this from day 1.
That said, someone on here recently had a grown button hen getting picked on by her cage mates and they separated her to let her wounds heal. They say she's tame enough to sleep in their lap now. But that's actually the first story I've read of an adult button becoming tame.
I never actually attempted to tame any of my buttons. Some will eat from my hand - I could probably get all of them to with a little patience. One of them becomes very curious when I clean her cage (I do this while she is in the cage) - initially she goes to the opposite end of the cage but it doesn't take long before she comes to check out what I'm doing. I can't touch her, but at least she doesn't panic every time I go near. She's probably the tamest one of mine.