In a large corpus (2.9 million tokens) of chat conversations, the impact was studied of Flemish adolescents’ social background on non-standard writing. Significant correlations were found between different aspects of social class (level of education, home language and profession of the parents) and all examined deviations from formal written standard Dutch. Clustering several social variables might not only lead to a better operationalization of the complex phenomenon of social class, it certainly allows for discriminating social groups with distinct linguistic practices: lower class teenagers used each of the non-standard features much more often and in some cases in a different way than their upper class peers. Possible explanations concern discrepancies in terms of both linguistic proficiency and linguistic attitudes. The findings emphasize the importance of including social background as an independent variable in variationist studies on youngsters’ computer-mediated communication.