READING SERIES 4th Grade Boys

    I am trying to get some books for my 4th grade library that
    the boys will be interested in. I have the Clementine,
    fairy and Just Grace series for girls along with a few
    others. My girls seem to know exactly what they want to
    read. Not so with a few of the boys. I have the Cabin Creek
    Mysteries and Bill Wallace's adventures but not quite sure
    what to add. Any suggestions? Thanks for your help. Happy