Assessing your strengths and areas of growth as an instructor is key, and this practice extends to teaching assistants, as well. How you present materials, how you communicate with your students, the kinds of feedback you provide for them (even if you are a grading teaching assistant and do not meet your students in person) all have an impact on the success of your students.
There are a number of methods to assess how you are performing your duties. It is important to recognize that assessment is an opportunity to strengthen and develop your skills, and is a staple of the vast majority of jobs you will hold in your professional lifetime. At Carleton University there is no formal evaluation of teaching assistants, so you are encouraged to take responsibility for your own assessment for the benefit of both your students, and yourself.
