I met with Grant Thornton officials at a university career fair. I was selected for an on-campus interview, which was preceded by a dinner event will all first- round interviewees. The first round involved a single interview with a Partner or Manager. The questions were very typical interview questions, trying to gauge behavioral traits.
It is VERY important that you have several questions to ask the interviewer. If you simply answer their questions and leave, you will not be called back. They want to see you are as interested in them as they are in you.
The second round began with an email invitation to an office visit (The Tuesday after the previous week's interviews). Before the office visit, candidates were invited out to dinner with Audit Associates and Seniors to relax and get to know the firm casually. Everything was fun and you had the chance to talk to other candidates in your field.
The office visit lasted from 10AM to 2PM. Candidates had 3 interviews with Managers and Partners. Each interview lasted 30 minutes. Each interview also seemed structured to address a part of the firm that was important (Work experience, personality, culture, community service, etc.). Again, make sure you have questions for the interviewer. They can be personal questions or about the firm, but just make sure you try to make a conversation out of it.
I received a phone call from one of the 3 interviewers informing me of my offer the next week.