This is exactly what DS had to do last year in second grade. Each week they were given a book to read and had to do a one page worksheet on it. Except the books they started with were *below* 2nd grade reading level!
We eventually struck a deal with the teacher that he could read other, more reading-level-appropriate books, instead. We chose stories from D'Aulaires' Book of Greek Myths; they were relatively short, interesting to DS (who was currently immersed in Percy Jackson), and at a much higher reading level.
Of course, DS still didn't want to do the assignment, but at that point it didn't matter.
We rebelled and homeschool now.
Seriously, though, I would ask the teacher if your DS can write his journal on something else. I think the point of the exercise when they're this young is to learn to write a summary of a book, not necessarily the books themselves.
