To investigate the effectiveness of the Geneva Back School (BS), we studied certain aspects of the retention of what was taught and the changes it induced in the patients. Thirty-nine BS patients were asked to draw their backs both before and after the BS. They were also asked to define the terms arthrosis and herniated disc once before the BS and twice after the program. Analysis of 78 drawings showed that the representation of the back was far from anatomical reality in both instances. The definitions of terms correlated poorly between patients and health care professional before BS. Teaching increased patient knowledge, but did not delete patients' prior notions. Our findings indicate that teaching strategies need to take into account patients' beliefs and knowledge. Health care professionals involved in BS programs should also be aware of the possible misunderstanding of medical terms. These factors may explain, at least partially, BS failures.