The Slime Squad books are great for encouraging young boys to read independently. (This isn't meant to be sexist: I haven't got any girls so don't know if a girl would like them or not. There is certainly a female monster member in the Squad who is feisty and likeable.) The books are full of jokes (the sort of yucky ones boys love) and are lighthearted and fast moving. If your ambition is to get a young boy reading independently I would strongly recommend the series.
