Many corpus linguistic studies have investigated classification of texts into genres and registers, but relatively few of these studies have looked at linguistic features in educational registers. From a pedagogical perspective it is important to determine whether certain linguistic features behave differently across registers within particular disciplines. The current study investigates conditionals, linguistic features that have extensively been studied in psychology, philosophy and education and can provide useful information on student reasoning and misconceptions. A series of corpus linguistic studies show that conditionals are more frequently used in a discipline like physics, regardless of the language mode (monolog or dialog), educational environment (tutoring or non-tutoring), formality (formal-informal) or interface (human-human, human-computer). Furthermore, evidence was found that students who are more proficient in physics use a higher number of conditionals than less proficient physics students. These findings have consequences for corpus linguistic studies on registers, for general pedagogy, and for physics pedagogy in particular.