Teachers often ask me what it means when a student scores poorly on the Verbal Comprehension Index of the WISC-IV (or a similar scale on another IQ test). The simple answer is that the scores don’t tell anything specific about how a student will perform in the classroom. However, classic intelligence theory claims that low Verbal Comprehension Index scores are an indication of poor crystallised knowledge.

Crystallised knowledge can be thought of as the information one acquires from one’s cultural and educational environment. There is an overlap between crystallised knowledge and semantic language skills. It develops largely as a result of formal and informal educational experiences and acquisition of this knowledge is heavily influenced by oral language skills and reading ability (Horn, 1994).

When students have a lot of crystallised information in their ‘mental hard-drive’, they not only make a good quiz teammate, but they are at an advantage when required to learn new information. This is because new learning is usually facilitated by prior knowledge (Engle, 1994). For example, it is much easier to learn about the concept of division when one already knows about multiplication. Likewise, it is easier to learn how to use an Apple computer if one is already skilled at operating a PC.

The student with a lot of crystallised information is also at an advantage when they have to perform higher-order reasoning functions. For example, it is hard to decipher the meaning of the first sentence below if one does not have prior knowledge of the Greek legend of Dionysius and the Sword of Damocles.

(a)   The threat hung over his head like the Sword of Damocles.

Likewise, one would have dififuclty understanding the second sentence below if one was not previously aware of the fact that La Paz is situated at high altitude and that flying into an area of high altitude without acclimatising is likely to lead to a mild bout of altitude sickness, a symptom of which is often a massive headache.

(b)   Tom spent two days in bed after flying into La Paz eating Aspirin like Jelly Beans.  

Prior knowledge is vital for classroom learning. For example, a student may not be able to understand a lesson on Hannibal’s role in the fall of Rome without prior knowledge of Hannibal, his elephants, and the Roman Empire. Lack of vocabulary (lexical knowledge) or in the depth and breadth of content (general knowledge) will also adversely affect written expression.

Other difficulties experienced by students who lack crystallised knowledge include reading comprehension problems despite having adequate word-reading skills. These students typically understand the ‘bare bones’ of the story. They can often retell the story, and they may be able to recall information that has been explicitly referred to in the story. However, they may not be able to draw meaningful connections to background knowledge and to draw inferences, both of which are crucial to developing the situation model upon which real understanding is based.  Students with adequate general knowledge, but poor vocabulary may read and understand well when they are reading about familiar topics. However, their comprehension suffers when reading about novel topics or when the text contains unfamiliar words.

Instructional strategies that may be useful include:

1. Audit the lesson and identify the pre-requisite crystallised knowledge. Check that the student has that knowledge. If not, teach it! Make use of parents or teacher aides or whatever you need to. Just make sure that the student is pre-taught the pre-requisite knowledge before the lesson begins. Otherwise, they’re just set up for failure.
2. Provide advanced organisers (e.g., an outline of material to be used in a lecture).
3. Teach previewing strategies to identify aspects of texts, such as headings, index, chapter headings, that give clues to the background and structure of the text.
4. Teach them how to identify and highlight key information.
5. Point out when important parts of lessons are about to be introduced (e.g., “this is the most important thing”, “if you only learn one thing today, this is it”).
6. Use “what we know, what we don’t know” strategies to help activate background knowledge before a lesson or reading a text.
7. Help the student develop writing plans (mind maps) that specify ideas, background details, and vocabulary to which they will need to refer.
8. Teach the student to use a thesaurus for writing.
9. Pre-teach new vocabulary in key content areas of the curriculum.
10. Write key terms on the board during lessons, particularly when introducing new concepts.
11. Simplify instructions and pre-define terms (e.g., a feldspar is like a little crystal in a rock. Now listen carefully, granite is a very hard rock that is composed of tiny feldspars; that is, it is made up of lots of tiny feldspars. Remember that feldspars are like little crystals in the rock.)
12. Consider providing the important components of a lesson in cloze format. Cloze sentences are sentences that have certain words missing. The job of taking notes is mostly done for the student, with the exception of key words that require them to consider the key points of the lesson or to access background knowledge.
13. Teach related vocabulary in groups (e.g., get, obtain, purchase, borrow, commandeer). Teach the students how these related words have similar, but sometimes different applications. Provide them with opportunities to compare and contrast these words as they learn them.