ABSTRACTWhat are the functions of psychologists at school? Is Educational Psychology the main Knowledge´s Area that supports their practice? We analyze ´mediating tools´ - socio-historical concept - psychologists use for their evaluations and interventions. What have those tools been constructed for? What do psychologists use them for now? We study analysis´ categories and units psychologists use when they cope with problems in the field. We compare the causes they attribute to learning problems with the causes that other social actors attribute to them: teachers and directors. We wonder about the object of psychologist´s study and its relation with different dimensions