"Unhelpful" teachers are not making life easy for chronically ill children in mainstream schools - more than a third of whom say they have been bullied or teased.
Half of the secondary pupils questioned by researchers from York University said teachers were the cause of "upset and difficulty".
Examples included incontinent pupils being refused permission to go to the toilet and teachers not believing pupils with ME and juvenile arthritis were ill.
Both teachers and pupils surveyed by researchers Suzanne Wright, Jane Lightfoot and Patricia Sloper agreed that the main problem was teachers' lack of information about medical problems - and their implications for school life.
Their research, presented to the conference, recommends health workers deal directly with teachers.
"At present, the way in which teachers respond to young people with chronic physical conditions seems highly variable, depending on whether they are aware of and understand the pupils' special health needs," says the paper.
"In order to improve this situation, professionals working within and outside of schools need to develop effective mechanisms for passing on information about special health needs to all teachers involved with the child."
Thirty-three pupils from 19 secondary schools took part in the study, which asked what support they needed from health and education services. They had a range of conditions, including asthma, diabetes, cerebral palsy, juvenile arthritis, ME, spina bifida, cystic fibrosis, renal failure and cancer.