I work in a small school with almost 50% SEN. We identify via pupil progress meetings. So I look at the data prior to the meeting, work out which pupils I want to ask about, as the teachers go through their lists I ask further questions and take notes and that generally identifies who’s having and who needs support / interventions, as well as pupils for me to observe who may be coping OK but maybe have a spiky profile and need some assessment whether for language, neurodevelopmental issues, specific learning disabilities etc etc