| Elaine O'Brien |
Anita of Rancho del Mar (age 9-12) family , historical |
| Robert C. O'Brien |
Mrs. Frisby and the Rats of NIMH (age 9-12) adventure , brilliant protagonist |
| Scott O'Dell |
Sing Down the Moon (age 9-12) adventure , historical |
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Zia (age 9-12) adventure , historical | |
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Sarah Bishop (age 10+) war , survival , family , historical | |
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Island of the Blue Dolphins (age 9-12) survival , adventure , historical | |
| Barbara Oconnor |
The Small Adventure of Popeye and Elvis (age 8-11) realistic , self-reliance , adventure , humor |
| Charles Ogden |
Rare Beasts (age 9-12) in: Edgar and Ellen Series humor , mystery |
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Tourist Trap (age 9-12) in: Edgar and Ellen Series humor , mystery | |
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Under Town (age 9-12) in: Edgar and Ellen Series humor , mystery | |
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High Wire (age 9-12) in: Edgar and Ellen Series humor , mystery | |
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Nod's Limbs (age 9-12) in: Edgar and Ellen Series humor , mystery | |
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Pet's Revenge (age 9-12) in: Edgar and Ellen Series humor , mystery | |
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Edgar and Ellen Mischief Manual: An Expert's Guide to Planning Perpetrating and Plausibly Denying All Pranks Great and Small But Mostly Great (age 9-12) in: Edgar and Ellen Series humor , mystery | |
| Kenneth Oppel |
Silverwing (age 9-12) in: The Silverwing Trilogy growing up , action , adventure |
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Sunwing (age 9-12) in: The Silverwing Trilogy growing up , action , adventure | |
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Firewing (age 9-12) in: The Silverwing Trilogy growing up , action , adventure | |
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Darkwing (age 10+) fantasy , action , adventure | |
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Airborn (age 10+) action , adventure , fantasy | |
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Skybreaker (age 10+) sequel to: Airborn action , adventure , fantasy | |
| Uri Orlev |
The Island on Bird Street (age 9-12) war , survival , historical |
| Wendy Orr |
Mokie and Bik (age 7-10) humor , family |
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Nim's Island (age 8-11) humor , friendship , adventure , nature , survival | |
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Nim at Sea (age 8-11) sequel to: Nim's Island humor , friendship , adventure , nature , survival | |
| Mary Pope Osborne |
Christmas in Camelot (age 7-10) in: Magic Tree House Series adventure , historical |
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Dark Day in the Deep Sea (age 7-10) in: Magic Tree House Series adventure , historical | |
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Eve of the Emperor Penguin (age 7-10) in: Magic Tree House Series adventure , historical | |
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Monday With a Mad Genius (age 7-10) in: Magic Tree House Series adventure , historical | |
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Mummies in the Morning (age 7-10) in: Magic Tree House Series adventure , historical | |
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Night of the New Magicians (age 7-10) in: Magic Tree House Series adventure , historical | |
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Polar Bears Past Bedtime (age 7-10) in: Magic Tree House Series adventure , historical | |
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Season of the Sandstorms (age 7-10) in: Magic Tree House Series adventure , historical | |
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Summer of the Sea Serpent (age 7-10) in: Magic Tree House Series adventure , historical | |
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Tigers at Twilight (age 7-10) in: Magic Tree House Series adventure , historical | |
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Winter of the Ice Wizard (age 7-10) in: Magic Tree House Series adventure , historical | |
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Standing in the Light: the Captive Diary of Catherine Carey Logan, Delaware Valley, Pennsylvania, 1763 (age 8-11) in: Dear America Series war , identity , letters/journal , historical | |
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My Brother's Keeper: Virginia's Civil War Diary (age 7-10) in: My America Series letters/journal , historical |