A great book on puberty is "Whats Happening To Me?" by Peter Mayle. At first glance you might think, because of the fun (and humerous) illustrations, that it's not what you have in mind. However, if you really look at it you'll find it's very informative and factual. It addresses puberty for both genders which is nice, because they have questions about what the opposite sex is going through as well. What I like best is that for this age group (my daughter is a very mature 10 year old), it gives age appropriate info. Not too much or too little, and the use of some humor lightens the touchy subject up enough for them to be a bit more comfortable... let's face it, we all need to have a sense of humor to go along with puberty!! I promise it isn't short on facts and answers! If he's especially shy about these subjects this book (which starts out reminding our youngsters that every adult, including their parents, has gone through puberty)may desensitize him some and help make it easier to discuss.
FYI - This book came to my attention because my God Daughter's Child Psychologist reccomended it. (She sees a psychologist because her mom deals with a serious chronic illness.)
~ T. K.