KanjiJLPT N5
Exam

exam, school, printing, proof, correction

Mnemonic

Before the big exam, students mingle under a towering tree, carving cheat notes into its bark. The tree's trunk is covered in scratched formulas from generations of students who mingle here before every exam.
Additional thoughts
Picture a campus tree whose bark is completely covered in tiny carved equations — a living cheat sheet built over decades of exam anxiety. Tree + mingling students = school exam setting.
Quick recall
Students mingle under a tree, carving notes before the exam.

Details

The keyword for 校 is exam. This kanji relates to the idea of checking, comparing, or proofreading — activities associated with careful examination and verification. It is also strongly associated with schools, as in a place where students are tested and evaluated. The underlying sense is one of scrutiny and correction, whether in an academic setting or in the process of reviewing written work.
On'yomi
こう、きょう