Advance organizers are used to relate prior information to new concepts.  They are part of  David Ausubel's subsumption theory that "contends that meaningful learning and permanent retention of material is a function of the stability of existing anchoring ideas" (Applin)   Ausubel
proposed four processes of meaningful learning:

                        Derivative subsumption. This describes the situation in which the new information I learn is an instance or example of a
                         concept that I have already learned. So, let's suppose I have acquired a basic concept such as "tree". I know that a tree has a
                         trunk, branches, green leaves, and may have some kind of fruit, and that, when fully grown is likely to be at least 12 feet tall.
                         Now I learn about a kind of tree that I have never seen before, let's say a persimmon tree, that conforms to my previous
                         understanding of tree. My new knowledge of persimmon trees is attached to my concept of tree, without substantially altering
                         that concept in any way. So, an Ausubelian would say that I had learned about persimmon trees through the process of
                         derivative subsumption.

                         Correlative subsumption. Now, let's suppose I encounter a new kind of tree that has red leaves, rather than green. In
                         order to accommodate this new information, I have to alter or extend my concept of tree to include the possibility of red
                         leaves. I have learned about this new kind of tree through the process of correlative subsumption. In a sense, you might say
                         that this is more "valuable" learning than that of derivative subsumption, since it enriches the higher-level concept.
 
 

                       Combinatorial learning. The first three learning processes all involve new information that "attaches" to a hierarchy at a
                         level that is either below or above previously acquired knowledge. Combinatorial learning is different; it describes a process
                         by which the new idea is derived from another idea that is neither higher nor lower in the hierarchy, but at the same level (in a
                         different, but related, "branch"). You could think of this as learning by analogy. For example, to teach someone about
                         pollination in plants, you might relate it to previously acquired knowledge of how fish eggs are fertilized. (Instructor notes P540)
 

The use of advance organizers makes sense.  We've learned that our brains retain information that is interconnected.  In order to help students make new connections it is imperative that we help them make associations between what they've already learned and how it relates to the new concept.  Students spend a huge amount of time memorizing facts in order to repeat that information on a test.  Once the test is over, often the individual facts disappear from memory.  If we can teach the "big idea" or main concept and then relate the individual facts to the big idea, students may retain more information, especially if it is called upon as prior knowledge in a later class.  "Most students study most material in a non-meaningful manner. They pack it in linearly and return it to us linearly on examinations without ever having truly processed the information internally. They are acting much like faulty tape recorders (they make more errors) and they don't understand what they are repeating." (Hayes)

What comes to my mind is how?  How do we pick out the main concepts and relate them to prior knowledge.  I am hoping to do my term paper on the creation of a workshop that I will be presenting for our staff.  How do I relate what they know already to what I'm teaching?  The experiences of the teachers will vary considerably, just as our students' experiences do.  How do we know what they know already?  The web site "What is the Big Idea?" gives good tips for finding the big ideas and using them to prepare your course or lesson.

We  spend a considerable amount of time on Venn diagrams that compare and contrast ideas and events.  This strategy helps students to make associations between two items.  "Advance organizers also have been described as bridges from students’previous knowledge to whatever is to be learned. They can call forth general organizational patterns and relationships already in mind that students may not necessarily think to use in assimilating the new material.  For example, before teaching the structure of state government, the teacher might have students recall the structure of the federal government with which they are already familiar and point out wherein the new structure to be learned will be alike or different from the structure already learned. Most of the text books now seem to use concept maps that help students relate information in a chapter." (Best Practices)   Making story maps and concept maps the students can see also help them to organize the new information.  For instance, teaching the difference between types of holidays could be displayed as:

(Corry)

This, of course , assumes that you have already taught the concept of "Culture" and they have prior knowledge of these holidays.  Students can now make a new connection between the word culture and cultural and visualize the difference between the holidays' origins.

Advance organizers are taught before a concept to show a relationship between the new knowledge and what they already know.  In order for this to work, we must be certain of what the students already know.  Unfortunately students do not all come with the same backgrounds.  While a large portion of your students may already understand a particular concept it is likely that one or two do not.  As I began to teach division this year I concentrated on the relationship division has to multiplication.  We manually divided beans into cups and reversed the process multiplying the number in the cups by the number of cups.  Most of my students quickly understood the relationship and were able to learn their division facts quickly by using their multiplication facts.  I had a student move into our classroom during this process.  This student did not have a clear understanding of what it means to multiply numbers and therefore was lost during this lesson. M. Corry states that, "To be useful, advance organizers themselves must obviously be learnable and must be stated in familiar terms."  If you were teaching a foreign student who had no  knowledge of Thanksgiving and Independence Day, it may be harder for them to make use of the diagram above.
 

References:
 

Applin, Anne, The Application of Language Acquisition Theory to Programming Concept Instruction

 Best Practices: What We've Learned About Good Instruction

Bruning, Roger, Cognitive Psychology and Instruction

Corry, M, Meaningful Reception Learning

Instruction Notes P540, Ausubel's "meaningful reception learning"

William A. and Carol A. Hayes, "What's the Big Idea"