Encourage pupils to keep a "positive diary" at the end of each lesson. On the inside of the front cover of their exercise books, ask them to title the page "What I have achieved today" and record at least one thing achieved during the lesson.
They could be specific points, such as a particular learning objective understood or more general comments about presentation or accuracy.
If the pupil retorts in a future lesson: "I can't do this subject" (maths, in my case) I encourage them to revisit their learning log. Or if I perceive a lesson to be challenging, I ask the pupils to spend a few moments reading their positive points at the beginning of the lesson.
Paul Ainsworth is deputy head at Belvoir High School in Bottesford, Leicestershire.