教学相长，汉语成语，意思是教和学两方面互相影响和促进，都得到提高。出自《礼记·学记》：“是故学然后知不足，教然后知困。知不足然后能自反也，知困然后能自强也。故曰教学相长也。”

《教学相长》（《礼记》节选）

虽有嘉肴，弗食，不知其旨也；虽有至道，弗学，不知其善也。是故学，然后知不足；教，然后知困。知不足；然后能自反也，知困；然后能自强也。故曰，教学相长也。

Even when there is good food, you will not know its deliciousness, if you don’t taste it; even when there is a good doctrine, you will not know its virtue, if you don’t learn it. Therefore, to learn makes us realize our deficiency, and to teach makes us know the difficulties. Having realized our deficiency, we may then come to reflect; having known the difficulties, we may be able to strengthen ourselves to overcome them. So, we say, to teach is to learn.