This year we've declared the boys are skilled enough at writing to handle (and now able to understand the concept of) thank-you notes. I bought a bunch of blank cards and just after Christmas sat down with them and had them write notes to their grandparents about the presents they received. Mackie's were very simple, Aran and Sasha's a little more complex. And then Sasha had his birthday a while ago. He got presents from his grandmothers, and I had him sit down again to write notes.
"Why I have to do this?" he demanded. "I already said thank you when I opened the present."
"Because Grandma and Granny went to the store and looked at several things and thought hard about what you might like. They chose presents carefully, then wrapped them and brought them all the way over here. All just for you. It's not too much for you to write a thank-you note to tell them how much you liked the gifts."
He thought about that, then nodded and wrote the letters without further comment. You =can= civilize a teenage boy--even one captured from the wilds of Ukraine!