On page 287 of the hardcover 1st edition of Ender's shadow, Bean "correctly" guesses that nine commanders had been graduated. It should be eleven or twelve.
Eleven: On page 286, we learn that "every toon leader and second" in Ender's army, plus Bean, was given command of an army in Battle School. Ender's army had five toons (and important plot point), meaning ten toon leaders and seconds. Including Bean, that means at least eleven new commanders. Since no new armies were created, eleven positions needed to "open up" for these new commanders.
Case for Twelve: The case for twelve hinges on counting Ender as a graduated commander. Since his army was dissolved and no new armies created, eleven PLUS Ender would need to be graduated to make room for the eleven new commanders.
Case Against Twelve: It may be unknown to the general student population (yet) that Ender was one of the graduated commanders. Since none of the principals saw the "notice" of graduated students, we don't know. Even if Ender's graduation was public knowledge, the speaker may have been excluding Ender, given the context of the conversation.
(1st Edition, hardcover) - Pg. 287