As an elementary science teacher, I primarily view my job as a vocabulary teacher because students need to know the science words before they can apply the concepts. As a result of this, I have begun to take the vocabulary teaching portion of my job more and more seriously.
A study that clearly shows the importance of background knowledge (vocabulary is an integral part of background knowledge) for comprehension was done by (Rect and Leslie, 1988). This study found that students who had low reading abilities and high content knowledge were able to comprehend a text better than students with a high reading ability and low content knowledge.
In short, the students with high content knowledge were able to “chunk” the important information together in order to retain it. While the students with low content knowledge needed to focus on every piece of information at the same time and as a result had a more difficult time visualizing and comprehending the content.
A scenario similar to this likely plays out in your classroom everyday. If you are teaching a unit on mass movement (landslides, flooding, etc), students will need to have background knowledge in the rock cycle and the environments you will be applying the new vocabulary to. Those that don’t will find their working memory to be overwhelmed as they will essentially be learning about the rock cycle, environments, and the new vocabulary simultaneously. This will lead to cognitive overload, poor performance, and worse, poor comprehension.
However, students that have strong background knowledge of environments and the rock cycle will likely understand and be able to apply the new vocabulary with much more confidence and accuracy than those without. The reason being, these students can focus on applying the new vocabulary to environments that they are familiar with. They have more background knowledge which reduces their cognitive load allowing them to focus on learning the new vocabulary.
In order to help my students who have less background knowledge, I try to give concrete examples of the vocabulary and its applications. The concrete examples are easily attainable for most students, and it gives them a reference point of a correct example (a worked problem). The students can then refer back to the concrete example as we apply the vocabulary to new circumstances.
An example of this would be with flooding. I would show a picture/short video of a flood in a place that had many different types of plants after giving students the definition. Then we would talk about how the flood impacted the environment (weathering, erosion, deposition). This example is more concrete because the students can see what is happening even if they are unfamiliar with the environment the flood is happening in. Then, as the class goes on, we will continually refer back to the video, explaining why flood produced those particular results.
This would then be the pattern I would want my students to apply to other situations. Ex: A flood in an environment without many plants. The students can check back to their notes to help them apply the vocabulary (flooding) to a new environment.
Having sufficient subject vocabulary is integral for students to succeed, as it allows for them to focus on the content (what you want students to learn) instead of getting lost in the delivery.