The image on the left comes from a t-shirt I bought at Beijing Normal University. The second image below is a picture of a large stone slab on the campus bearing the same Chinese characters. This is the motto for BNU, which was founded as a teacher's college. When I asked people in China to tell me what it means they told me that there is not just a single translation.
Answers.com gives the following: Study well, teach others. Be your best, set an example.
This site says: Behave to be the model, learn to be the master.
Another variation: studying to teach and acting to example
The following is my own choice for best translation, sort of the consensus opinion of those I talked to at BNU about what the motto means in English.
Learn, so as to teach others. Act, to serve as an example to all.