I'm basically convinced by his arguments, although I do think that schools need to continue to dedicate some time to analysis of what is read in order to develop critical thinking skills. In my experience, focusing solely on fact-accrual leads to "smart" people who don't know how to think things through and express their arguments clearly.
Now to apply some insights gained from reading this book to teaching my daughter--1) Keep reading to her, lots, and expose her to intelligent and interesting books (not those lame leveled-readers that are boring). 2) Cover many content fields and try to stick with each field for more than one book/video at a time so that she is able to focus on an area of content knowledge for a while. 3) Teach her anything that interests her, even if I didn't "study" it until high school (obviously, teach it at a level that is appropriate for her). 4) Expose my children to higher-level vocabulary in context and rarely use slang with them. 5) Find good meaty source books for learning about history, science, art, etc.; formalistic inquiry-based and/or nonsubstantive textbooks will not help her develop much subject knowledge.
Here is a good "money quote" from The Knowledge Deficit:
Breadth of knowledge is the single factor within human control that contributes most to academic achievement and general cognitive competence.