Your response could include something that may have been a challenge in the past, which you have taken steps to rectify. It is important to be truthful, they will be testing your honesty. In addition, they will be checking to see if you provide a weakness that is critical to success in the position. For example, the interview will likely end quickly if you answer you have a difficult time management the classroom. The key to answering the question is to turn a negative into a positive.