Abstract This study applies additive Multi-Dimensional Analysis (MDA) (Biber 1988) to explore the linguistic characteristics of ‘school English’ or ‘textbook English’. It seeks to find out how text registers commonly featured in English as a Foreign Language (EFL) textbooks differ from comparable registers found outside the EFL classroom. To this end, a Textbook English Corpus (TEC) of 43 coursebooks used in European schools is mobilised. The texts from six textbook register subcorpora and three target language corpora are mapped onto Biber’s (1998) ‘Involved vs. Informational’ dimension of General English. Register accounts for 63% of the variance in these dimension scores in the TEC. Additional factors such as textbook level, series and country of publication/use only play a marginal role in mediating textbook register variation. Textbook dialogues score considerably lower than the Spoken BNC2014, whereas Textbook Fiction scores closest to its corresponding reference Youth Fiction Corpus. Pedagogical and methodological implications are discussed.