Think of chunking as the ability to mentally package information using pre-existing background knowledge for easy recall. Chunking is useful because the human mind can only keep and manipulate about seven things in working memory. Chunking allows you to get around this biological limitation.
Here's an example from Willingham of chunking in action.
[R]ead through this list one time, then look away and see how many of the letters you can recall.Chunking is a useful tool, but, as you can see, chunking requires you to have background knowledge in order to activate. In the example above, you need to know what the FBI, CNN, CBS, CIA and NCAA are in order to chunk the letters.
There were 16 letters on the list, and most people can recall around seven—there is not sufficient space in working memory to maintain more than that. Now try the same task again with this list.
NCAAMuch easier, right? If you compare the two lists, you will see that they actually contain the same letters. The second list has been reorganized in a way that encourages you to treat C, N, and N as a single unit, rather than as three separate letters.
Another critical use for background knowledge is for making inferences and connections while reading text. Here's an example from Hirsch:
Cognitive psychologists have determined that when a text is being understood, the reader (or listener) is filling in a lot of the unstated connections between the words to create an imagined "situation model" based on domain-specific knowledge. This situation model constitutes the understood meaning of the text. Take, for example, this passage from my book What Your Second-Grader Needs to Know:Of course, there's much more to it than that and I suggest you , if you haven't done so yet, read all the articles I've linked to. Let me try to oversimplify. You need to know a lot of stuff in order to quicly learn more stuff, quickly process and analyze the new stuff, remember the new stuff more easily, helps you solve problems, and allows you to think lesss (by not having to derive everything).
In 1861, the Civil War started. It lasted until 1865. It was American against American, North against South. The Southerners called Northerners “Yankees.” Northerners called Southerners “Rebels,” or “Rebs” for short. General Robert E. Lee was in charge of the Southern army. General Ulysses S. Grant was in charge of the Northern army.
Potentially, this passage is usefully informative to a second-grader learning about the Civil War—but only if he or she already understands much of what’s addressed in it. Take the phrase "North against South." A wealth of preexisting background information is needed to understand that simple phrase--going far beyond the root idea of compass directions, which is simply the necessary first step. The child needs a general idea of the geography of the U.S. and needs to infer that the named compass directions stand for geographical regions. Then a further inference or construction is needed: The child has to understand that the names of geographical regions stand for the populations of those regions and that those populations have been organized into some sort of collectivity so they can raise armies. That’s just an initial stab at unpacking what the child must infer to understand the phrase “North against South.” A full, explicit account of the taken-for-granted knowledge that someone would need to construct a situation model for this passage would take many pages of analysis.
The trick is, of course, getting all that knowledge into your head in the first place. This'll be the topic of my next post, but I'll leave you with this teaser. Schools do a miserable job at teaching facts, if anything they deride the entire process and consciously avoid teaching facts in favor of teaching students how to "learn how to learn," which you know, if you've read the articles I linked to, is a crock.