Unconscious biases can be thought of as the shortcuts the brain takes to make life easier. Psychologists Daniel Kahneman (2011) and Amos Tversky explain that unconscious biases arise because humans have two thinking systems: a fast, automatic (unconscious) system and a slower more deliberative (conscious) system. The first system can be thought of as the one that helped humanity to respond rapidly to threats and deal with lots of information. The second thinking system takes more effort and is slower; it is the system used when marking a piece of writing or buying a computer. The automatic system uses 'rules of thumb' or heuristics to help process information and make decisions. Unfortunately, these heuristics can be wrong and are what lead to unconscious biases. In primary schools, unconscious bias can lead teachers to treat children differently without realising that they are doing so. In this article, the author outlines the possible influence of unconscious bias on primary science.