The post-school change in English skills of former students from upper secondary education was analyzed in this exploratory study. Methodologically, the underlying interlanguage analysis, the focus on active language competence, and the prospectively examined 'attrition' time spans should be emphasized. The results demonstrate the long-term effects of the English skills learned in school. Two and a half years - and in two cases even 15 years - after graduation, the interlanguages had only changed 'cosmetically', not functionally. Apparently, a complex language system had developed through a learning process of at least seven years, which made it resistant to forgetting and allowed it to be maintained for many years even without frequent language contact.