I applied for a co-op positing during my senior year. I got a call about scheduling a phone interview and then I was interviewed by 4 people on the specific day of the interview. They called me and the interview lasted for almost 45 minutes. The interview was not hard. If you know your resume well then you should be fine. I was only asked questions from the resume about school projects, no other technical questions. The people who interviewed me were really nice, so I got lucky there. I was offered the co-op position after one week of the phone interview. They do not require on site interview for students.