Frustrated!!!!!

I am very frustrated wrapping up the end of the year with my students. I have a student in my classroom that is very negative and disrespectful to me and others in the classroom. This brings down the attitude of the students and me as well. He joined our class after winter break and has changed the whole dynamics of the classroom. I have never had such a negative second grade child in my classroom before and am not sure how to deal with this behavior. We were taking the MAP Math test today and he had a very hard time taking the test. He would ask me questions and I couldn't answer them for him. He then just would say things like "then I will just guess or fine I will get them all wrong". I continually reminded him that he needed to try his best and if he didn't know the answer to pick the best one and move on. I have tried to ignore the behavior, but have a difficult time with that when he is influencing the behavior of other students in the class. Does anyone have any suggestions?