Robert Rothman, writing for the Harvard Education Letter, shares insight and research governing the inclusion of text complexity in the Common Core State Standards. In short, high school students are practicing with texts that are well below what they will be asked to read in college or career. He notes:
Writers of the standards say that students’ ability to comprehend the kinds of texts they will encounter in college and the workplace is perhaps the most critical factor in ensuring that they are prepared for postsecondary life. Yet research cited in the standards found that, while the complexity of texts in entry-level college courses and workplaces has held steady or increased slightly, the complexity of texts used in high schools has declined over the past few decades.
You can read the entire article here.