The common core standards will require a lot more changes than just shifting to harder text (though I think that change will be the biggest one for most teachers).
The standards also increase the instructional emphasis on informational text, disciplinary literacy, multiple text, close/critical reading, technology in literacy and language, writing about text, and some other areas that teachers are not necessarily ready for yet. When I say that there is a shift of emphasis, I am not saying that there are some new items on some previously uncovered topics; what I am saying is that these standards require or presuppose substantial shifts across large numbers of the standards--at all levels and often in all of the various parts of the common core standards. For example, if you look at the reading, reading foundations, speaking/listening, writing, and language sections, you'll find that about 10% of all the items emphasize multiple text. That means all teachers are going to need to be resourced and supported in dealing with an aspect of teaching that most haven't learned much about. The same is true of these other areas of concern.
Today, I made a webinar presentation on these challenges at for the International Reading Association. If you would like a copy of the powerpoint, just click on the title of this blog entry and you'll have it. Good luck.
Oh by the way... I was just reading an interesting study that Rollanda O'Connor and her colleagues published in the Journal of Psychology in 2010. In that article they tested the impact of text difficulty differences on various reading outcomes and found no differences due to text difficulty. That is certainly not evidence that we need to go harder with the texts that we choose, but it is just one more piece of evidence showing that we have been too complacent and compliant in our over-reliance on matching kids to books. That just isn't as important as some "experts" would have you believe.