Strong claims have regularly been made in the popular media about the alleged negative effects of young people's language use in written exchanges via digital media (what is known as textese). This is especially believed to affect their reading and writing skills. However, the scientific research literature has hardly confirmed such effects. Its conclusions are generally based on cross-sectional comparisons between individuals who differ in how much they exchange written messages via digital media. In contrast, the present study examines to what extent per-country changes in the prevalence of online chatting coincide with changes in the reading literacy of consecutive student cohorts. This approach presents a novel perspective. The findings relate to data from the Programme for International Student Assessment (PISA) surveys conducted during 2000–2018. The data analysis showed a strong correlation between variations in per-country patterns regarding the spread of online chatting during 2000–2018 and changes in the reading literacy of 15-year-olds. Countries with low chatting prevalence in 2009 showed substantial improvement in reading literacy from 2000 to 2009. These trends typically reversed to declines when after 2009, online chatting prevalence sharply increased in those countries. A contrasting pattern applied to countries with high chatting prevalence in 2009 and decelerating growth in online chatting afterward.