How should an employer validate one's skills/knowledge?

What is your opinion on how a potential employer should "properly" validate that one truely has the knowledge and skills that his/her certification claims that he/she does?

Going a bit deeper…how far should the employer go in validating the candidate's knowledge and skills? Should a list of 25, 50, etc questions be enough? Should two or more interviews be enough? What about an on-the-spot required lab?

Thanks for your feedback.

Personally I don't hold with giving interviewees a technical test consiting of 20 or 30 questions. What counts is the real-world experience they've had on the CV - if they've clearly been doing the job for a reasonable period and haven't been chain-fired that is 50% of the assurance you need. The other 50% comes from a good second interview. The first interview is the usual weed-out of psycopaths and time wasters, then a second interview can be more of a chat over the technology areas the job involves and the individual's claimed past experience. Any interviewer worth their salt can easily expose a charlatan or paper-only engineer.
Case in point was a second interview I had for a network/support engineer post where we sat down at the guy's desk and after the pleasantries he said "this is my PC; tell me about it". So I jumped on there and went through the hardware, the defrag state of the hard drive, the way the network was set up, showed him what was in the run key in the regisrty etc. Then he took me into a wiring closet and repeated the question, and a third time with the server suite. Very effective.

Speaking as someone who only one "technical" qualification (HNC in Business (IT)), which I got over 10 years ago, I'd have to agree with the Bishop. I've got loads of "on the job" experience, but would probably struggle with a test sheet, and think that the Interview is a much better way of weeding people out. The idea of doing a "practical" Interview appeals to me.

Many years ago, I worked for a Company called Royal London Insurance, which involved selling financial products etc. When I did one of he interviews, the guy interviewing me said " I don't like interviews, because people can say what they think I want to hear. So, we are going to have a chat, and I'll find out what I need to know that way. During our "chat" he gave me some little job related tests to do. At the end of about an hour or so he finally said "you'll do just fine in this job". So, since then, I've always believed that a good interviewer can get everything they need just by talking to the candidate.

Other than the case when the employer intentionally wants to find a Junior instead of a Senior. I think I agree that a good interview/interviewer can do well in uncovering experience. Well, even for the junior case a good interview would expose the candidates mental abilities I guess. Prepared questions might be good when you have a large scale employment plan for tens or hundreds of candidates and you simply don't have enough time to interview all. So they take a test, and then whoever passes takes an interview. Not saying this is flawless, but at least, that's what is been done here in some oil companies.

Back in year 2000 I was a grad student looking for job, when I ran into this IT learning institute where my only experience was at programming. So the guy had a small chat with me and immediately drove me to the class room and told me to start to teach him!!! (Visual Basic). I think, it was that moment where I knew that I hatted teaching. The guy obviously didn't get a word of what I was saying and never called me after. I'm glad he didn't. Not only he became sure that I'm not a good teacher but I did.

It's ironic now that although I'm a system admin at my university, I still have to teach students too. Some how I developed a skill that students like, but I still hate it's nature.

solo in the classroom... but you sound a good teacher in writing well.. well...

solo in the classroom... but you sound a good teacher in writing well.. well...

Thanks... hope so