Shakespeare's writing is very demanding on the reader. Almost every line, every word even, requires reflection. It certainly isn't easy, but once understood the content is so interesting that no one ever regrets the effort - I've never seen it anyway. But its difficulty is important in itself, because it improves the skills that constitute reading comprehension, which is undoubtedly as important (at least) as any other academic ability.

So there it is: the literature that is the most interesting and the one that produces the greatest increase in academic performance is one and the same. What, you may be wondering, are the arguments against its use in high school? I'll summarize (and try to demolish) them tomorrow.