The following comments by international TAs indicate ways in which students' varied backgrounds can be taken into account while teaching. As Americans say, it's important to put yourself in the shoes of the students. You can spend a few hours in the first week with them to review material and catch them up, especially if these students are willing to learn. I myself always disliked a teacher who does not know the potential of the students and the problems the students are facing. Let them know that your target is for them to learn something out of this class.
Students understand the same question from different ways.
When I know students, I know what they need, and I am better able to explain. It's important to encourage students. All students want to get something from the class, so you can still find some way to help them get more. Although it is important for the TA to endeavor to meet the diverse needs of students, some students will need more help than can reasonably be given during class and office hours. Most colleges and universities have student services such as academic and study skill centers or a tutorial office that these students can be referred to.