Illiteracy specifies an issue to be investigated by the study of adult development: the interaction between the acquisition of the numerical system and the pre-existent ones, the verified functions and the reasons for the persistence of notation errors. A study conducted with two students from literacy classes aged 20 and 32 years old is reported. The first student used to fix bicycles and the second was a bus fare-collector . Ten sessions focusing on the logic mediation of numerical representation were conducted. The raising of personal problematic situations was used as a means to restructure thought and orientate the students' attention towards the procedures. The results reveal difficulties to use numerical notation and the rules to calculate; to establish relationships between the notation of operations and a particular situation; to recognize the sequence and numerical composition; to identify that addition and subtraction are operations that belong to the same conceptual field. The progress promoted by the process is shown and the educational practice that adults are submitted to is discussed.
adult cognitive development; school initiation; numerical notation
