The job interview process usually starts with a resume and a cover letter, followed by a round or two of interviews. For some employers, however, this may not be enough for them to make a sound hiring decision. Employers who want to see more of a job candidate might ask that candidate to do a working interview.
Details of the Working Interview
In short, a working interview is the time for a job candidate to show an employer what she can do. Often, that involves having the job candidate do the duties she'd do during her day-to-day work. If she's not able to jump in and do the exact duties -- for example, if she needs extensive training on a particular machine to do the job safely -- she may be asked to talk about how she'd do certain tasks or to otherwise demonstrate her expertise in a situation that's not "live." A working interview can last anywhere between a few hours to several days.
It's Actually Trial Employment
In the eyes of the law, the working interview is actually a trial employment period, not unpaid training before hire. It may be no big deal for you to work a few hours in order to get the job, but the employer must pay you at least minimum wage for that time.
Before you start doing any tasks as part of the working interview, the employer will likely ask you to fill out employment paperwork -- the same he'd ask of any provisional employee. This doesn't necessarily mean you have the job; it just means the employer is following the letter of the law and adding you to the payroll for this working interview period.
Preparing for the Working Interview
You probably won't be perfect at everything that's thrown at you at the working interview, but you can certainly prepare. Find out what tasks you'll be responsible for doing by poring over the job posting and asking questions during your initial interview, then do research to brush up on those skills.
Get plenty of sleep the night before, and bring a few snacks to ensure you don't get low blood sugar from the busy day. While the employer will be evaluating your skills, he'll also be looking for enthusiasm and a can-do attitude. Showing that you're positive and willing to learn can help overcome any gaps in knowledge or skills that may reveal themselves during the working interview.
If you're an employer, treat the working interviewee like any new employee. Have the person fill out the same W-2 paperwork and employment eligibility paperwork you use for other employees. At the end of the day, give the candidate a check for the hours she "worked" as part of the working interview. Do this even if you plan to hire the person, as you may be paying the candidate a different amount than you'd pay her as an employee, and it makes things cleaner.