Like many kids, my 9 y.o. son is a voracious reader. He seems to have plateaued in terms of the level he reads at - Harry Potter, Jules Verne, the Ender Books, Little House books, Percy Jackson, The Hunger Games...so he reads at a fairly high level, but given the choice will not choose anything more demanding than the young adult level that only if the topic is of interest.
My voracious reader son had a 9 month hault in reading progress at the same age. It drove me crazy because he kept complaining about not having good books despite any efforts. Finally, his sister was reading an above level book that surprized him and he started progressing again.
During this time I think he was studying humor in his easier books. Maybe he wanted to relate better to other kids.
Sorry, I can not offer advice in the other areas.
