Who wrote this poem acquire new knowledge while thinking over the old you may become a teacher of others?

The poem you are referring to is actually a proverb, not a complete poem. It is a popular saying often attributed to Confucius, the famous Chinese philosopher.

Here's a slightly more complete version:

"By three methods we may learn wisdom: First, by reflection, which is noblest; Second, by imitation, which is easiest; and third by experience, which is the bitterest."

The part you quoted is a distillation of the first two methods, emphasizing the importance of contemplation and learning from others.

It's a powerful reminder that true knowledge requires both reflecting on past learning and seeking guidance from others. By doing so, we can eventually become teachers ourselves, sharing our wisdom with the world.