Big, Middle, Small — School Levels

Japanese names its schools by size. Stack 小 (small), 中 (middle), and 高 (high) onto the school kanji 校 and you get 小学校 (shōgakkō, elementary school), 中学校 (chūgakkō, middle school), and 高校 (kōkō, high school) — while 大 (big) pairs with the 学 from your last set to make 大学 (daigaku, university). Five kanji that unlock every rung of the Japanese school ladder.

大 is ダイ in 大学 (and おお in 大きい, big). 中 is チュウ — middle — and reappears in 中国 (China). 小 is ショウ here, but ちい in 小さい (small). 校 and 高 are a コウ homophone pair: 校 is the building, 高 is the quality (high/tall). Mind the small-tsu gemination in 学校 (gakkō) and 高校 (kōkō).