I often find myself searching for full-text pieces for my students to use in class. Here are several resources I have found.
40 Excellent Short Stories for Middle School http://www.mrswatersenglish.com/2014/05/40-excellent-short-stories-for-middle-school/
Short Stories for Middle School Students-Click the tabs across the top of the page for additional lists. The Christmas list is pretty cool. http://americanliterature.com/middle-school-short-stories
Smithsonian TweenTribune-Each full-text article has a short answer question that goes along with it.