Events and conditions in pupils' lives which make it difficult or less likely that they will be able to learn effectively; for example, hunger, emotional upset, illness, family separation, and bereavement. On the other hand, barriers might include less obvious factors such as inflexible school systems or an inappropriate curriculum. Bullying, too, has a profound effect on some victims' ability to learn. Existing and potential barriers to learning may go undetected, particularly in those cases where the root cause is linked to aspects of young people's lives outside school. Where good home–school partnerships exist, these barriers can more easily be overcome. Barriers to learning may arise unexpectedly and may be of a permanent or temporary nature. For this reason it is important that schools and other educational institutions remain vigilant in order to spot changes in learning and behaviour patterns. This enables appropriate support and interventions to be implemented promptly, and for planning and assessment to take into account the type and extent of the learner's difficulties.