DBQ's are Document Based Questions that are used in certain Advanced Placement classes as well as in a number of state assessments. Because DBQ's make students write essays using a number of primary source documents, DBQ's require our students to think, analyze, and use and refine their literacy strategies. For this reason, in my experience as a middle school social studies teacher, the use of DBQ's are not just for higher level students only but are important for all students.
I have found that the best way to help prepare students for Document Based Questions is to have students examine primary source quotations within many of my seventh grade lessons, and have students discuss, question, make inferences, and answer questions from those sources. A difference between the use of DBQs in my middle school classroom and what one might see in an AP course is that I use fewer documents (two or three rather than five or six), and I use quotations and excerpts from those documents. Regarding these points, the Internet allows teachers to find virtually any primary source that they wish to use in their classroom, but I also believe it necessary to use ellipses and brackets to transform those quotes into something with which my seventh graders can deal. Of course my students know that when they see brackets in a quote it means I have slightly altered a word or phrase so that they can better understand it, and on my SMART Board I will show them the original source. For an excellent discussion of simplifying and focusing primary sources to make them accessible to our students I strongly recommend Sam Wineburg and Daisy Martin's article, "Tampering with History: Adapting Primary Sources,"  in the September 2009 issue of Social Education .
Two strategies I often use when presenting students with primary sources are Response Groups and Mystery to help my students read through and analyze primary source documents. Both utilize small cooperative learning groups so that my students can substantively converse on the documents. I teach World history, and my units often use archaeological finds to explore particular eras; for example, in teaching my unit on ancient Rome we begin with an exploration of Pompeii. In this unit, I use Response Groups to have students read portions of Pliny the Younger's letter to the historian Tacitus on the explosion of Vesuvius. I later use the Mystery strategy to have groups read through and categorize the graffiti and statements written on the walls of Pompeii to get a glimpse of daily life in a typical Roman province. In keeping with the cooperative learning principal of individual accountability, as with any DBQ, students' will individually write an essay on what they have learned from the primary source documents and quotes.
DBQ's can add to the engagement of your students while improving their literacy skills, and reading words from the past adds a special air of excitement to the work.