I find many students who do not understand the need for quotation marks around direct quotes.  They provide an in-text citation, which is great, but there is nothing to tell the reader that this is a quotation.  They often don't mean to plagiarize, but that is what they are doing, and I sometimes wonder if they have been taught properly what it is they need to do. 

One area that usually confuses my students is that APA is different from MLA.  Often students have been taught MLA in high school.  The form is similar enough to confuse them.  Remember that in APA you write author’s name, a comma, and the year in parenthesis like this (name, year).  APA also uses a p. instead of just the page number for a page.

http://en.wikipedia.org/wiki/APA_style