I had a great response from my last blog Mixed Matched Middle Readers  for mature readers. So, I wanted to share a few more titles on this level that I think you will also enjoy. Please make a comment below if you are interested in a specific genre  and would like additional suggestions.
Tracing Stars by Erin E. Moulton
In a small seaside town during the summer before sixth grade, Indie Lee Chickory tries to follow her older sister's popularity advice by working backstage on the upcoming community theater musical and by not revealing that she is looking for her beloved pet lobster and becoming friends with "loser" Owen Stone. A charming novel about sisterhood, self-identity, and friendship.
Return to Exile E.J. Patten
Eleven years ago , a shattered band of ancient monster hunters captured an unimaginable evil and Phineas T. Pimiscule rescued his nephew, Sky, from the wreckage of that great battle. For eleven years, Sky Weathers has studied traps, puzzles, science, and the secret lore of the Hunters of Legend believing it all a game. For eleven years, Sky and his family have hidden from dark enemies while, unbeknownst to Sky, his uncle Phineas sacrificed everything to protect them. For eleven years, Sky Weathers has known nothing of that day. But on the eve of Sky's twelfth birthday and his family's long-awaited return to the town of Exile, everything changes. Phineas has disappeared, and Sky finds himself forced to confront the mysterious secrets he's denied for so long: why did his family leave Exile on that day so long ago? What, exactly, has Phineas been preparing him for? And, the biggest mystery of all, who is Sky really and why does everyone want to kill him?! Featuring an action-packed plot that covers the gamut of every monster you've never heard of (not to mention weird powers and weapons made out of garbage), Return to Exile is brimming with boy and girl appeal and is a gem for reluctant young readers. And, with a diverse assortment of well-aged monster hunters in the cast, this series will be a hit with adults young and old as well.
Ruby Redfort Look into My Eyes Laura Child
Thirteen-year-old Ruby, a genius code-cracker and daring detective, gets an anonymous call setting a challenge that leads her to the headquarters of Spectrum, a highly secret anti-crime agency that needs her help to crack a code, but soon Ruby uncovers dastardly plans of the Fool's Gold Gang. Just take a classic comedy, add heaps of breathtaking action, and multiply it by Lauren Child's writing genius, and what have you got? A summer read
The False Prince Jennifer A. Nielsen
The thrilling first book in a brand-new trilogy filled with danger, deceit, and hidden identities. Sage, an orphaned thief, is one of four boys chosen to participate in a lethal contest. After being plucked from the streets by a nobleman named Connor, Sage learns that Connor plans to choose one of the orphans to impersonate a long-lost prince in the hopes of averting a civil war.
Ghost Knight Cornelia Funke
Eleven-year-old Jon Whitcroft and new friend Ella summon the ghost of Sir William Longspee, who may be able to protect Jon from a group of ghosts that threatens him harm from the day he arrives at Salisbury Cathedral's boarding school. Includes historical notes.
The Secret Tree  Natalie Standiford
After sixth grader Minty discovers a secret tree with a hollow trunk that holds the secrets of everyone in the neighborhood, Raymond, a new boy drawn to the tree and Minty start watching their neighbors. A sweet story of a tree that's literally filled with secrets.
Wonder  R.J. Palacio.
Auggie Pullman was born with a facial deformity that prevented him from going to a mainstream school, until now. He's about to start 5th grade at Beecher Prep, and is nervous about being the new kid at school. The thing is Auggie's just an ordinary kid, with an extraordinary face. But can he convince his new classmates that he's just like them, despite appearances?
A Hero for WondLa  [Book Two] Tony DiTerlizzi
The highly anticipated new illustrated novel in the New York Times bestselling The Search for WondLa series. Before the end of The Search for WondLa , Eva Nine had never seen another human, but after a human boy named Hailey rescues her along with her companions, she couldn't be happier. Eva thinks she has everything she's ever dreamed of, especially when Hailey brings her and her friends to the colony of New Attica, where humans of all shapes and sizes live in apparent peace and harmony. But all is not idyllic in New Attica, and Eva Nine soon realizes that something sinister is going on, and if she doesn't stop it, it could mean the end of everything and everyone on planet Orbona. Three illustrations trigger a 3-D Augmented Reality flying game that mimics action in the novel. Featuring an abundance of lavish two-color illustrations and spot art throughout and introducing a host of remarkable characters that reinforce the importance of friendship, A Hero for WondLa has all the hallmarks of a classic book of the future.
Storybound  Marissa Burt
Shy, twelve-year-old Una Fairchild is suddenly transported by a mysterious book into the Land of Story, where characters from books hope to be cast into a tale of their own, and Una attends the Perrault Academy while trying to discover why she is there.
Above World Jenn Reese.
In a future of high technology and genetic modification the Coral Kampii, like legendary mermaids, live isolated from the Above World, but when the devices that allows them to breathe underwater start to fail, thirteen-year-old Aluna and her friend Hoku go to that forbidden place to find help.