You know the other thing I always had trouble with? Convincing people that Australia actually was bigger than Greenland. That damn Mercator Projection! I always preferred globes to flat maps even back then.
I remember this back in 3rd grade too-- people simply wouldn't believe me when I told them Greenland was smaller than South America and Australia....I actually didn't know what the Mercator Projection was until the following year, but I did notice the lines of latitude stretched out the farther north you went and I used that to figure out that Greenland was no way anywhere near as big as either of those continents.
The other thing I clearly remember was that people didn't believe me when I told them that that little hook part at the extreme north point of Minnesota (near Lake of the Woods) was the northernmost point in the 48 states.....noooo, they said, Maine is further north, see, it's higher up! Nevermind the fact that latitude lines are curved and clearly show northern Maine isn't as north as northernmost Minnesota is.