This chapter explores how simple biological considerations such as hunger and tiredness can impact on children’s behaviour, and to identify simple interventions based on this knowledge that can prevent episodes of negative behaviour from occurring. It introduces the role of temperament, the concept of ‘executive function’ and how children’s brain development over time can have implications for their behaviour through the development of skills such as impulse control and self-regulation. Biological theories of behaviour argue that development is a biological process, and so behaviour is seen as primarily determined by genetic potential. One consideration that may not come to mind in educators is that simple biological considerations like hunger, tiredness or physical discomfort can play an important role in behavioural outcomes for children. The development of executive function and self-regulatory skills depends on the biological maturity of the child, and the process is heavily influenced by environmental experiences.