"I started at a temp job a few weeks ago. I feel confused about how I should approach this job in terms of my professional appearance. I assumed I should dress up a little (it is business casual) so I generally wear black pants and a button-up shirt. Many of my co-workers wear flip-flops and do not dress professionally, clearly breaking the dress code. Even my boss wears a zip-up sweatshirt over her dress clothes. My question is this: As the temp (hoping to get a job with the company when the temp position is over) should I dress well and follow the dress code or blend in with my co-workers and dress down? My worry is that I will seem arrogant or unapproachable (especially since my education level is above most of my co-workers) by dressing nicely but at the same time I do not want to damage any opportunity to further my position at this company."
While normally I'm not a fan of assumptions, you did make the right one here. It's always a good idea to dress one notch up than the office standard when applying for and taking on a new job. Your dress style sounds like a good match for a casual office, even for one whose standards may have slipped over time.
As a temp, you need to meet the standards of two companies: the one you temp for, and the temp agency itself. While part of your job as a temp is to respect the office culture you're entering, you also need to represent the professional standards of the agency. As a representative from the agency, it would be expected that you follow the official dress code of the company you're temping for. So, sticking to your basic business casual attire is a better choice than busting the dress code and dressing down to fit in. At the end of your stint at this company, you’ll be rated on your professionalism, including your appearance. Positive ratings are only to your advantage, especially if you move on to temp at another company.
Do you think people at this office find you approachable right now? If that's the case, then your clothing isn't an obstacle to fitting into their culture. No matter how your coworkers or your boss dress, when it comes time to make a hiring decision, the company is more likely to choose someone who looks professional (which subliminally translates into "capable") than someone who doesn't.