Ok - well field trip to the bank might be a way to start. The American Banking association probably has a website that explains it as well. Try 'How things work' website for ideas.
Have you explained where baby's come from? - that usually his high on the interest meter.
But here's what I would did - (Looking back I think I unknowingly hothoused this subtest without realizing it, because it's what I find interesting. We did "Where babies come from at age 3" - for fun.
Tell me what kind of Television you all watch. I would reccomend recording some episodes of the Simpsons, if your son isn't too young for them, and watching them with him and stopping at the jokes to see if he 'gets' them and to explain them if he doesn't.
For those of you who are gasping - just be glad I didn't reccoment watching 'South Park!' That's the 'Advanced Version.'
Of course you can use any show you like, I just love being controversial. My son literally did go through a Simpsons and then a South Park immersion experience, where we Tivo'd a bunch of episodes, and he watched with his hand on the pause button, demanding explainations of evey joke. And yes, I did warn him that if I heard "Eat my shorts" exit his mouth that the shows would got to time out for a good long while.
Love and More Love,
Grinty
