Several parts combine into one character.

Phonetic-semantic compound: 木 (wood / tree) + 交 (cross / interlock, providing both phonetic and a hint of meaning). The original meaning was startlingly grim: a wooden stocks or yoke — a punishment device that bound criminals' feet between crossed boards. Over centuries, the meaning shifted from "place that physically corrects a body" to "place that intellectually corrects a mind" — and that became "school". Identical across 繁體 / 新字体 / 简体.

While the etymology is jarring, it preserves a coherent thread: 校 always refers to a place where people are formed, corrected, or set right. The proofreader's mark 校正 (jiàozhèng / kōsei, "to correct text") and 校訂 (proofread) preserve the original "set right" sense; 学校 (xuéxiào / gakkō, "school") extends it to education.

Mandarin has TWO tones for 校: — xiào (4th tone): school. 学校 (xuéxiào, school), 校园 (xiàoyuán, campus), 母校 (mǔxiào, alma mater), 校长 (xiàozhǎng, principal). — jiào (4th tone): to correct / proofread. 校对 (jiàoduì, to proofread), 校正 (jiàozhèng, to correct). Learners often skip the second tone, but it appears in publishing and academic contexts.

Japanese: on-reading コウ (kō) is dominant — 学校 (gakkō, school), 小学校 (shōgakkō, elementary), 中学校 (chūgakkō, middle school), 高校 (kōkō, high school — short for 高等学校), 校長 (kōchō, principal), 校歌 (kōka, school song), 校庭 (kōtei, schoolyard), 母校 (bokō, alma mater), 校正 (kōsei, proofreading). One of the most school-life-saturated characters in Japanese.

Memory aid: wooden crossbars — once binding feet, now containing a campus.