Agreed, however there're is one misconception here, rooted in reality, not necessarily research... Less complex info at elementary level AND teaching has shifted to test prep, drill-and-kill which makes students successful on a TEST, not necessarily measuring learning - real learning, critical thinking, etc. Not showing mastery, per se. If students do not master basic, fundamental skills, as in coding/decoding re literacy, less likely they will be able to keep up in HS. This is getting overlooked. Just as CCSS is supposed to staircase and build upon these common skills, each year, in a more complex way.