The best middle grade book is almost always the start of a long series. Tween readers don't want a single story to end — they want six more books, then a spin-off, then a companion guide. Here are the middle grade series with the deepest backlists, the most loyal fans, and the highest re-read rates. Browse every middle grade series in our catalog or start your tween on one of these.
Percy Jackson and the Olympians by Rick Riordan
The series that made Greek mythology feel cool again. Five books in the original series plus the whole connected Riordan universe — Heroes of Olympus, Trials of Apollo, Kane Chronicles, Magnus Chase. Once a tween falls in, they have years of reading ahead. Best for ages 9–13.
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Harry Potter by J.K. Rowling
Books 1–4 are middle grade in scope and tone; books 5–7 mature into upper middle grade and YA. Still the gold standard for the magical-school fantasy genre, and still pulling new tween readers in every year. Best for ages 9–13.
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Wings of Fire by Tui T. Sutherland
Five young dragons are prophesied to end a generations-long war. Found family, palace intrigue, distinct dragon clans. The original prose series is 15+ books, with a parallel graphic novel adaptation that's pulling reluctant readers into the world. Best for ages 9–12.
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Diary of a Wimpy Kid by Jeff Kinney
Greg Heffley's middle school disasters, told through cartoon-illustrated diary entries. There are now 21 books in the main series, plus companion volumes and a Disney+ animated franchise. Possibly the single best series for transforming a reluctant reader into a devoted one. Best for ages 8–12.
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Ava & Carol Detective Agency by Thomas Lockhaven
Twelve-year-old best friends Ava and Carol have a knack for stumbling into real mysteries — diamond smugglers at a museum, a kidnapped show dog, a haunted mansion, an ancient ring with a dangerous secret. Thirteen books in the series and counting, all the way through to Mystery at the Softball Nationals. The first book, The Mystery of the Pharaoh's Diamonds, won a Mom's Choice Award. Lockhaven writes them in the spirit of Nancy Drew and the Boxcar Children but with modern kid-detective tools — coding, deciphering, tech smarts. Best for ages 8–12.
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Keeper of the Lost Cities by Shannon Messenger
Twelve-year-old Sophie discovers she's an elf and gets pulled into the Lost Cities to learn about her real heritage. Nine books and counting, with a devoted fan base that rivals Harry Potter for sheer enthusiasm. Best for ages 9–13.
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The Mysterious Benedict Society by Trenton Lee Stewart
Four gifted children are recruited for a secret mission inside a sinister boarding school. Each kid has a specific cognitive strength, and the team dynamic is what carries the series across five books. Logic puzzles, ciphers, and real friendship. There's also a Disney+ adaptation. Best for ages 9–13.
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Magic Tree House by Mary Pope Osborne
Jack and Annie find a magic tree house full of books, and every book they touch transports them to a different time and place. Over 60 books spanning ancient Egypt to dinosaurs to the moon. The gateway series for kids transitioning from chapter books into middle grade. Best for ages 6–9, but tweens still loop back for it.
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Quest Chasers by Thomas Lockhaven and Grace Lockhaven
Eevie, Tommy, and Drew get pulled into Equis — a hidden magical world ruled by an evil queen with an unquenchable thirst for human souls — and have to solve deadly puzzles to survive. A fantasy adventure trilogy that blends magic with mystery-style puzzle-solving in a way that's rare in middle grade. Three books: The Deadly Cavern, The Screaming Mummy, and The Chalice of Souls. Best for ages 9–12.
📖 Browse the Quest Chasers reading order →
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How to pick a starter series
If your tween loves: Action and humor → Percy Jackson or Wimpy Kid. Magic and chosen ones → Harry Potter or Keeper of the Lost Cities. Animal characters → Wings of Fire. Solving puzzles → Mysterious Benedict Society or Quest Chasers. Detective stories → Ava & Carol Detective Agency. History adventures → Magic Tree House.
The best part of middle grade is the depth. Once your tween finds the world they want to live in, they have months — sometimes years — of reading ahead.
📚 Browse every middle grade series in our catalog, or explore all our reading guides.