This is a lesson plan which you can use to teach 4th or 5th grade boys about puberty. I used it to teach my own students and it was a great success. You will need the Puberty for Boys Diagrams to teach this lesson. They're also free.
These are the diagrams which you need to use with the Puberty for Boys Lesson Plan. The lesson plan is free as well.
Please make sure each student has a copy of these diagrams or have every two students share a copy.