"Sometimes people's brains get stuck and think about one thing too much. This isn't good for the brain because brains should think about many different things to keep learning and growing. Right now your brain is getting stuck on trains a lot. We need to make sure your brain learns about a lot of things, not just trains, so we will sometimes ask you to stop talking about trains and thinking about trains for a while."
Then you can propose the solution. "The trains will be available for 20 minutes a day" or "the trains will be back in November" or whatever you are choosing.
He will probably think it is the end of the world, but it won't be if you hang in there and stick to whatever plan you articulated.
Some people find the obsession ends faster and more thoroughly if the thing goes totally away for some months, rather than being a limited-availability item, which tends to increase its value.
I think in Michelle Garcia Winner's teaching materials she calls the stuck brain "rock brain." We like to call it "stuck" because it implies that a change of state is possible (getting "unstuck").
DeeDee
p.s. favorite enforcement phrase: "not available," as in "the trains are not available now." Nicely neutral, heads off some of the more personal lines of argument about mean parents, just states a fact.
Last edited by DeeDee; 09/20/11 07:19 PM. Reason: added p.s.