The primary objective of having a portfolio is to develop rapport with an employer during an interview or performance evaluation. The ability to use it wisely is the ultimate litmus test! Don't expect the employer to look through the entire portfolio or wait for them to ask you about it.
Instead, use your portfolio selectively. Before the interview, determine which examples you would like to show and know where they are located in your portfolio. Develop a brief "story" or concrete example that corresponds with your work sample. Focus on how you achieved positive results. Participating in a practice interview with a career counselor or a friend can be excellent preparation to help you become comfortable using your portfolio.
Spend time developing rapport with the employer before you introduce your portfolio. Respond first to the interview question being asked. If you have a portfolio item that can back up the credibility of your response, inform the interviewer you have an example to share with her. Don't risk asking whether she would like to see the example (many employers have not had experience with portfolios, and you may be told "no"). Pull the item out of your portfolio and hand it to the interviewer. Handing it to her ensures your item will be reviewed and can effectively engage everyone involved in a group (or panel) interview.
Avoid overusing the portfolio; it is better to show too few examples than too many. I advocate the "peek-a-boo method" -i.e. keeping your portfolio closed when you are not using it in order to pique interest.
Don't ever leave your portfolio behind after the interview. You don't want to give up control over how it is used or risk losing it. Instead, you may want to develop a "mini-portfolio" - a smaller version with a few work examples you could leave with the employer.
Carmen Croonquist, Director of Career Services at The University of Wisconsin-River Falls is an expert on portfolio development. She has conducted presentations on the topic nationwide.