Ender's Shadow Series, Book 1, "Bean's past was a battle just to survive. His success brought him to the attention of the Battle School's recruiters, those people scouring the planet for leaders, tacticians, and generals to save Earth from the threat of alien invasion. Bean was sent into orbit, to the Battle School. And there he met Ender...." (Amazon).
Option two is Speaker for the Dead. While this is technically the second book in the Ender series, it takes place decades after the war, unlike the Shadow series. A more mature and psychological book, an older Ender must face his past, risk his life, the lives of three cultures, and try to stop history from repeating itself.
Ender's Game Series, Book 2, Speaker for the Dead, "In the aftermath of his terrible war, Ender Wiggin disappeared, and a powerful voice arose: The Speaker for the Dead, who told the true story of the Bugger War.
Now, long years later, a second alien race has been discovered, but again the aliens' ways are strange and frightening...again, humans die. And it is only the Speaker for the Dead, who is also Ender Wiggin the Xenocide, who has the courage to confront the mystery...and the truth" (Amazon).
Love Ender's Game? Wondering what to read next? There are two parallel series to choose from. Ender's Shadow is book one in a series that begins at the same time period as Ender's Game. While Game follows Ender's life and point of view, Shadow follows Bean's. Arguably more intelligent than Ender, Bean arrives at Battle School after Ender has already been chosen as the one, but it turns out that Bean is needed, too. One problem, Bean has to learn what comes to Ender naturally-- empathy. Without love or trust, will anyone follow him?
Remember- I came across Card and the Ender's series' because a student recommended it to me about 20 years ago. It was the first book a student gave to me to read. Since then hundreds of student have read Ender's Game and I have read about 13 books a year recommended by students. My board is always open to student recommendations! I take the homework you assign to me seriously, and I am always on the look out for good books to share, or possibly, to add to our official curriculum. Sophomore year's student recommended book? The House of the Scorpion. Look for it forth quarter next year!