Here are some recommended books from ReformedPerspective.ca that may be appropriate for readers in middle school. As of the time of this writing, I haven’t read them myself. Please use the links to check the reviews out for yourself, and let me know if you think the recommended age should be adjusted!

titleauthorlinkageverdict
The New Has ComeFarenhorst, Christinehttps://reformedperspective.ca/the-new-has-come/Middle SchoolRecommeded
Hostage LandsBond, Douglashttps://reformedperspective.ca/hostage-lands/Middle SchoolRecommended
Hobgoblins: A Novel on John BunyanBond, Douglashttps://reformedperspective.ca/the-hobgoblins/Middle SchoolRecommended
The RevoltBond, Douglashttps://reformedperspective.ca/the-revolt-a-novel-in-wycliffes-england/Middle SchoolRecommended
Bell MountainDuigon, Leehttps://reformedperspective.ca/bell-mountain/Middle SchoolRecommended
Hidden: Stories of War and PeaceFarenhorst, Christinehttps://reformedperspective.ca/hidden-stories-of-war-and-peace/Middle SchoolRecommended
Afterwards I Knew: Stories from the First and Second World WarsFarenhorst, Christinehttps://reformedperspective.ca/afterwards-i-knew-stories-from-the-first-and-second-world-wars/Middle SchoolRecommended
The Farm at the Center of the UniverseGonzalez, Guillermo and Jonathan Witthttps://reformedperspective.ca/farm-center-of-the-universe/Middle SchoolRecommended
FoundHaddix, Margaret Petersonhttps://reformedperspective.ca/the-always-war/Middle SchoolRecommended
The Secret CodeHartman, Coenhttps://reformedperspective.ca/the-secret-code/Middle SchoolRecommended
SlackerKorman, Gordonhttps://reformedperspective.ca/rediscovering-gordon-korman/Middle SchoolRecommended
Operation Do-OverKorman, Gordonhttps://reformedperspective.ca/rediscovering-gordon-korman/Middle SchoolRecommended
The FortKorman, Gordonhttps://reformedperspective.ca/rediscovering-gordon-korman/Middle SchoolRecommended
Urchin of the Riding StarsMcAllister, M.I.https://reformedperspective.ca/urchin-of-the-riding-stars/Middle SchoolRecommended
Wambu: The Chieftain’s SonPrins, Piethttps://reformedperspective.ca/wambu-the-chieftains-son/Middle SchoolRecommended
Wambu: In the Valley of DeathPrins, Piethttps://reformedperspective.ca/wambu-the-chieftains-son/Middle SchoolRecommended
Wambu: Journey to ManhoodPrins, Piethttps://reformedperspective.ca/wambu-the-chieftains-son/Middle SchoolRecommended
Scout: The Mystery of the Abandoned MillPrins, Piethttps://reformedperspective.ca/scout-the-mystery-of-the-abandoned-mill/Middle SchoolRecommended
MedallionWatkins, Dawn L.https://reformedperspective.ca/medallion/Middle SchoolRecommended
ShieldWatkins, Dawn L.https://reformedperspective.ca/medallion/Middle SchoolRecommended
The Hyperinflation DevastationBoyack, Connorhttps://reformedperspective.ca/the-hyperinflation-devastation/Middle SchoolRecommended (with Caution)
The Seraph’s Path (The Seraph Book 1)Dykstra, Neilhttps://reformedperspective.ca/book-review-the-seraphs-path/Middle SchoolRecommended (with Caution)
The Great EscapeFarenhorst, Christinehttps://reformedperspective.ca/the-great-escape/Middle SchoolRecommended (with caution)
The Always WarHaddix, Margaret Petersonhttps://reformedperspective.ca/the-always-war/Middle SchoolRecommended (with Caution)
In the Hall of the Dragon KingLawhead, Stephenhttps://reformedperspective.ca/in-the-hall-of-the-dragon-king/Middle SchoolRecommended (with Caution)
The Warlords of NinLawhead, Stephenhttps://reformedperspective.ca/in-the-hall-of-the-dragon-king/Middle SchoolRecommended (with Caution)
The Sword and the FlameLawhead, Stephenhttps://reformedperspective.ca/in-the-hall-of-the-dragon-king/Middle SchoolRecommended (with Caution)
The GiverLowry, Loishttps://reformedperspective.ca/the-giver-2/Middle SchoolRecommended (with caution)
Mount MajesticTrafton, Jenniferhttps://reformedperspective.ca/fantastic-preteenteen-fiction/Middle SchoolRecommended (with Caution)
ArrowWatkins, Dawn L.https://reformedperspective.ca/medallion/Middle SchoolRecommended (with caution)

These may (or may not) be a bit young for Middle School, but nevertheless, I want to included them in case they’re a good fit for your middle school kiddo:

Wings of Dawn (Magnus)Brouwer, Sigmundhttps://reformedperspective.ca/wings-of-dawn/Mid-late Elementary, Middle SchoolRecommended
Made in HeavenComfort, Rayhttps://reformedperspective.ca/made-in-heaven/Mid-late Elementary, Middle SchoolRecommended
The Adventures of Lancelot the GreatMorris, Geraldhttps://reformedperspective.ca/5-great-chapter-books/Mid-late Elementary, Middle SchoolRecommended
Sir Balin the Ill-FatedMorris, Geraldhttps://reformedperspective.ca/5-great-chapter-books/Mid-late Elementary, Middle SchoolRecommended
Sir Givret the ShortMorris, Geraldhttps://reformedperspective.ca/5-great-chapter-books/Mid-late Elementary, Middle SchoolRecommended