Very colorful textbooks with lots of illustrations may also not increase learning.Wow-- someone should alert math textbook developers.
And the makers of Junior High/High School Planners. Our schools/districts try to "sell" us these crazy high school planners as necessary for the child to be organized. They are so crammed full of of stuff (school spirit stuff, ads) that it's hard to find the calendar planner stuff and thus IMO very hard to use.
I have a small collection of contemporary textbooks (probably 20 or so if I include the ones my kids brought home this year). With a few exceptions (the ones written by bona fide subject experts), the new ones are mostly the same: they're jammed with brightly colored distractions including icons, photos, sidebars, and other things, and are short on actual
text. The math books are the worst. They tend to have sentences instead of paragraphs.
I was looking through a new 6th grade Earth Science book I have recently, and it had the same problem. Every chapter had a chunk of 8-10 pages of pure garbage that was all packed together. It made it very hard to find actual information in the book, let alone extract it.
Compare with older textbooks and good newer ones (e.g. Walker, Physics, 2009 edition). These books are full of text, and illustrations or photos are only used to clarify concepts.
IMO, the bright colors and lack of information are what you get when you stop paying reasonable royalties to expert authors and start outsourcing to cheap labor. You get what you pay for, which is flashy marketing and not much else.