We learn about and appreciate God's magnificent order and design in creation as we study them in the classroom. We can still honor God studying them even if we never put them into practice outside the classroom. History should be studied, among other things, to see God's providence at work and to understand God's agenda for the world. I can see a lot of English grammar being learned if the students were to get involved writing a school newsletter or journal, yet it doesn't change the fact that the vast majority of it is more practically learned in the classroom. The thrust of Adams's book would have been much more helpful if he had promoted the idea of projects as supplemental to classroom study instead of replacing classroom study altogether as he does.
Many Christian families choose to homeschool their children and have had great success.
But there is total silence in the book concerning home schooling. It is not even discussed as an option. This method is obviously too monumental a task for a single family. It is based on his sanguine notion that young students are out in the world doing projects and ministries with adequate discipline and self-motivation. Grading is a means to keep them responsible and consistent in their learning.