The study reported on in this paper uses corpus data in order to examine how upper-intermediate to advanced EFL learners from a wide range of mother tongue backgrounds perform a number of rhetorical functions particularly prominent in academic discourse, and how this compares with native academic writing. In particular, it is shown that one of the problems experienced by EFL learners is that they tend to use features that are more typical of speech than of academic prose, which suggests that they are largely unaware of register differences. Four possible explanations are offered to account for this register confusion, namely the influence of speech, L1 transfer, teaching-induced factors and developmental factors.