A PARADOX of education is that presenting information in a way that looks easy to learn often has the opposite effect. Numerous studies have demonstrated that when people are forced to think hard about what they are shown they remember it better, so it is worth looking at ways this can be done. And a piece of research about to be published in Cognition, by Daniel Oppenheimer, a psychologist at Princeton University, and his colleagues, suggests a simple one: make the text conveying the information harder to read.

Dr Oppenheimer recruited 28 volunteers aged between 18 and 40 and asked them to learn, from written descriptions, about three “species” of extraterrestrial alien, each of which had seven features. This task was meant to be similar to learning about animal species in a biology lesson. It used aliens in place of actual species to be certain that the participants could not draw on prior knowledge.

Half of the volunteers were presented with the information in difficult-to-read fonts (12-point Comic Sans MS 75% greyscale and 12-point Bodoni MT 75% greyscale). The other half saw it in 16-point Arial pure-black font, which tests have shown is one of the easiest to read.

Participants were given 90 seconds to memorise the information in the lists. They were then distracted with unrelated tasks for a quarter of an hour or so, before being asked questions about the aliens, such as “What is the diet of the Pangerish?” and “What colour eyes does the Norgletti have?” The upshot was that those reading the Arial font got the answers right 72.8% of the time, on average. Those forced to read the more difficult fonts answered correctly 86.5% of the time.

The question was, would this result translate from the controlled circumstances of the laboratory to the unruly environment of the classroom? It did. When the researchers asked teachers to use the technique in high-school lessons on chemistry, physics, English and history, they got similar results. The lesson, then, is to make text books harder to read, not easier.