This paper investigates teaching behaviour and seeks to overcome methodological difficulties associated with research about school improvement. Using reflective writing techniques, teachers recorded their own novel behaviours associated with improvement. The behaviour of teachers who are trying to improve pupil learning is seen to include specific pedagogic behaviours, but also teacher-learning behaviours. What teachers considered valid evidence of "improvement" is seen to differ from many definitions currently in use. Changed teacher behaviours included: observing others teach; target-setting; changing teaching or assessment techniques; increased use of data; showing an interest in the views of pupils and fellow teachers; sharing data with pupils; encouraging each other to read; and writing reflectively. Many of these behaviours involved teachers becoming more vulnerable to pupils, or to each other. Questioning their own beliefs in the light of research findings, and in the light of feedback from colleagues, is also interpreted as vulnerability.