And he literally does the final genocide in hope that it would grant him expulsion on medical grounds - because he didn't know the battles were real.

Speaker for the Dead is the book that the author originally wanted to write. Ender's Game was written as a prequel for it.

To clarify, yes, Speaker for the Dead is the book Card wanted to write, but he found he had to write Ender's Game first to lay the groundwork. And he did. He wrote them in that order (Ender, Speaker). A prequel usually refers to a work produced later that comes chronologically before.

I see, thanks for clarifying.

Seriously? I have read them in exactly that order. In comparison with Speaker for the Dead, the Ender's Game seems little childish...

Maye because Ender is a child there and the other books are him growing up and being wise.