ATA hires mostly in the early part of the year, as part of their annual budget process. The recruiter that I dealt with was very professional and friendly. After an initial phone screen, she connected me with the hiring manager.
The next interview was a phone interview, with the hiring manager and two senior employees in the department. They started off with a number of typical behavioral interview questions - nothing too unexpected. They then proceeded into technical questions related to embedded systems development - nothing too intense, but certainly the kind of things that would filter out someone who didn't know what the job was about. Apparently I knew enough to proceed to the next step.
The next, and final, interview was on site with the same 3 interviewers. Questions again were first behavioral and then technical, and were deeper. Behavioral questions were some of the tougher ones, but not abstract and meant to throw you for a loop. Although I didn't necessarily have great answers for them all, they weren't so tough that I was at a complete loss. The technical questions ranged from low-level programming to high-level problem solving.