Success at school increases self-esteem. Any difficulty will have consequential effects on the psychological health of the subject. The conditions now prevailing in the educational institutions (mass schooling without any individual orientation before the end of college) oblige the teenager to submit to teaching methods and to the school system. School can reveal the subject's personal problems (anxiety, phobia or depression), but may equally create pathology by not recognising the heterogeneity of individual development and differences in cognitive functioning. In adolescence, the ego is particularly vulnerable. Anything that may induce its instability can create behavioural problems (instability, aggressiveness, inhibition) or problems of thought (anxiety links, difficulties in abstraction). In order to cope with such a haemorrhage of the ego, the adolescent may have recourse to certain behaviours (e.g. use of drugs leading to dependence). So it is important the know well the links between school failure and behavioural problems or drug consumption because, in one way or another, by their sanction or by lack of motivation, these situations will lead very quickly to school disengagement, which in turn leads to the breakdown of the ego.