Test writing, teaching

Ok, some mundane news just to keep the blogging ball rolling. Tonight I'm writing a test for my students. They're in mathayom 6, which is their last year of high school. The test I'm writing is a pretty dry use-this-word-in-a-sentence vocabulary test, and it's a retest of one that most of them bombed just before Christmas. They do more or less okay at remembering the meanings of words, but if I ask them to make a sentence with it I consistently get nasty surprises like:
1) worthwhile: "Global warming is the worthwhile problem."

I get sad when my students don't know stuff. Next year I'm going to throw so much more mud at that wall...