Ken to Mahou to Gakureki Shakai: Zense wa Gariben Datta Ore ga, Konse wa Kazemakase de Jiyuu ni Ikitai

The third son of a viscount, Allen Rovene has hated studying since the day he was born. And no wonder—after suddenly regaining the memories of his past life at the age of twelve, he realizes he spent the entirety of his previous life hunched over a desk, studying like a studyholic! Reborn into his dream world of swords and magic, he's determined to make the most of his second chance by ditching the books and living a carefree, unburdened life—until he realizes the path to freedom has a detour in the form of the most renowned school in the kingdom: the Royal Knight and Mage Academy of Yugria. To become the magic-wielding, sword-swinging adventurer of his dreams, Allen's going to have to repurpose his well-honed study skills toward one goal—passing the hellish entrance exams and heading to the Royal Academy!

(Source: J-Novel Club)