When is an illustration worth ten thousand words?

We often hear this saying “a picture is worth a thousand words”, but just how true is it in the context of science education?

I encountered this highly cited paper written by Richard E. Mayer from University of California, Santa Barbara and Joan K. Gallini from University of South Carolina. They conducted an experiment to investigate when the picture illustrations will likely improve students’ learning.

In the experiment, students were asked to read passages explaining how different scientific devices work. They were divided into four treatment groups. The passages they read contained either:

①no illustrations, only texts (control);

②device with labels for each part (parts illustration);

③device with labels for each major action (steps illustration);

④device with labels for each part and each major action (parts-and-steps).


Figure 1: Illustration of a pump system with parts illustration, steps illustration, parts-and-steps illustration.

Before reading the passages, students were assessed on their prior knowledge of the topic and they were classified as either “low-knowledge” learners or “high-knowledge” learners. After reading the passages, all of them took three types of post-tests: knowledge recall, problem-solving and verbatim retention (meaning to remember the sentences word-for-word).

The study results show that the parts-and-steps illustration helped students to recall concepts, but not facts. It enhanced students’ ability in creative problem solving, but not memorizing sentences word-for-word. In addition, results show that these improvements are mainly obtained for students with a low prior knowledge.

The findings are consistent with what I have experienced both as a student and as an educator. When I was a student, I loved seeing my textbooks filled with colorful illustrations, not only because the illustrations are attractive, but also because I found the text information boring and abstract. Sometimes I got lost when reading a long passage of explanation. Picture illustrations, on the other hand, are more engaging. They allowed me to apply what I have read and actively construct the knowledge and concept in my mind.

Being a science educator now, I am also keen to use illustrations to help my students understand. For instance, during my lab sessions, I often draw the procedure flow on the white board, allowing students to visualize the bigger picture. Diagrams like this help them to appreciate each procedure as part of an experimental design, instead of disjointed steps. I found that students can recall the experimental flow more clearly and perform tasks better after seeing the diagram illustrations.

Although the paper was published in 1990, which was more than 20 years ago, its findings still have relevance today, when we are increasingly putting more emphasis on developing students’ critical thinking and problem-solving skills. Illustrations help students to understand better the concepts and enhance their problem solving skills. And this is especially true for those who lack prior knowledge on the topic. Hence it remains a useful tool for promoting students’ understanding of scientific material.


Mayer, R.E., Gallini, J.K. (1990).  When is an illustration worth ten thousand words? Journal of Educational Psychology. 82 (4), 715-726.


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