One year my son did use an Explorer's Bible Study that covered the book of Job. He loved that year's study, but then the next year when I got another from Explorers he hated it. So, we just went back to simply reading the bible.

He does read some spiritual books each year (like this year he'll read Mere Christianity). I didn't start that type of reading until he was a teen. In fact, this year will be the first year my younger son, soon to be 14yo, will read a spiritual based book like that (I'm thinking God's Will God's Best...maybe).