This is not an in-depth, philosophical treatment of writing (though some may say the author accomplishes it indirectly), but an example after example fun activity tool for teachers--sprinkled with nuggets of wisdom throughout. For those who find such things useful (I don't necessarily) this latest edition includes rubrics, portfolio assessment, and writing across the curriculum. Even if you find only a small portion helpful, the purchase is worth the price. Suitable for primary through middle school.
The Creative Teacher: Activities for Language Arts (Grades 4 through 8 and Up)