Earlier research has confirmed that loneliness is a universal phenomenon, experienced by children and adults. Few reports have been published of investigations of experiences of loneliness among school children in the United Kingdom. The aim of this study was to investigate how the ideas about loneliness held by British children develop during the early years in school. Evidence was sought for developmental trends in the content of interview responses about loneliness from 85 children aged between 5- and 10-years-old. Throughout this age range the children who were interviewed demonstrated willingness and ability to discuss and describe loneliness. They portrayed loneliness as a negative experience and a multidimensional phenomenon, experienced in a range of locations including school. There were developmental trends in the consistency with which children differentiated between feeling lonely and simply being alone. The youngest children were less likely than others to attribute a feeling of loneliness at school to being separated or excluded from friendship groups. Evidence was found of children’s ability to describe psychological loneliness, attributing this to feelings of rejection, difference, lack of familiarity, or personal loss. Implications for future research and for teachers and educational psychologists are discussed.