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: