Correlation is not probability. You can't compare them at all. Flipping a coin for each student would produce a correlation of 0, far lower than the correlation of 0.56 cited above. Have a look at some plots of data [1] with different correlation coefficients to see how dramatic it can be. Note the difference between r = 0.00 and r = 0.60. That's about what we're dealing with here.

[1] http://www.bwgriffin.com/gsu/courses/edur7130/images/twelve_...