book recommendation? -- sci fi for a 5th grader?

not fantasy, but science fiction. apparently my memory serves me very badly; i was all excited to give her ender's game because i liked it when i read it decades ago and it was about a kid and everything ...but when i picked it up to reread it i realized how much more brutal it was than i remembered. anybody have a recommendation for something a little more age-appropriate but still challenging for a 10-year-old strong reader and a good story? she's already read the mushroom planet books and the wrinkle in time books.
love tuck everlasting but she already read that, too.

i was thinking about asimov books too, munny,but i just can't remember what age group they might be appropriate for. i'll check it out, and the other suggestions, too. thanks everybody.
 
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