教学相长

jiào xué xiāng zhǎng

teaching and learning help each other grow

Character by character

教jiào
teach

学xué
learn

相xiāng
mutually

长zhǎng
grow

教学相长，学生的问题也让我学到很多。

Teaching cuts both ways: my students' questions teach me a lot.

Tone: positive (praise).

From the 《礼记》. Polyphones: 教 jiào, 相 xiāng, 长 zhǎng.

Learn it in context

This idiom and thousands more are in Learn Chinese with Bao, with audio, pinyin and drills that make them stick.