The use of Wikipedia in Social Studies has long been forbidden in my personal experience. I've never know a class that allowed students to cite a wiki as a source. That said I've never started a research paper in the last 10 years without first consulting Wikipedia to set myself up with a general understanding of what I'm researching. Hoping that at least 80% of what I read was accurate before I began looking into books, articles, and other sources. Often I found in situations where I had to take a side on an issue that I could at least get a feel quickly for different sides of arguments and pick on or two to dive deeper into.
Am I arguing that a student can just look at a Wikipedia article and write their whole report? Not at all, just as no one would argue that a student could consult a single encyclopedia and write a whole report. All I'm saying is that there isn't a real reason that students can't use Wikipedia like they would any encyclopedia. Now the first thing people say in response to that is that anyone can edit an article and therefore you can't be certain they are accurate. This is true but also doesn't hold water. You see Wikipedia has hoards of people that exist soul to check every edit made to an article, these same people can ban users from editing pages, and lock pages that are being targeted for regular abuse. More often than not one finds that Wikipedia pages are most likely accurate and flagged accordingly for bias or lack of evidence. Thus depending on the resources available to a student it may be that a Wikipedia article is far more accurate than the 50 year old encyclopedia in the school library. I agree that we don't want to see an in text citation from Wikipedia but as I said, using it as a jumping off point and method for getting a general idea about a subject seems completely legitimate. Besides we all know that students are looking at Wikipedia any way and I'd rather a student honestly list their sources in the bibliography than have to lie about it and start down a road of plagiarism.