Off the top of your head, what do you remember having been taught about the topic sentence?

I should have listed this request down in the education forum, but I was afraid it might have been overlooked.

My freshmen have been working on increasing their writing fluency this year. Although we work on nitty-gritty grammar problems (and mysteries), these students haven't had to worry about writing topic sentences. However, we will focus very much on formal essay paragraph structure during February, and I'm trying to figure out lots of different ways to approach this most certainly dreaded terrain in which the students must discipline their thinking.

The topic sentence is taught in a variety of sometimes contradictory ways. I've been surfing the Web all morning and have found several contradictions, which are actually fun to come across. But one thing is evident: topic sentences are here to stay and professors are frustrated when reading papers in which students have written poorly-constructed topic sentences. One writer on the Web wrote that topic sentences are like traffic signs through the terrain of an essay. I thought that was pretty good. Highway markers may have been an even better image.

Anyway, if any of you could jot down a thought or two about what you recall about learning to write a clear topic sentence, I will read here with interest and will report to my freshmen the writers on 'the word board,' as I refer to it, have written.