Computer-assisted learning can be either single-thread or multi-thread. When learning is single-thread, the learner works with one learning unit at a time; having passed or failed the "current" learning unit, the learner then moves on to the next learning unit. When learning is multi-thread, several learning threads may be "developing" simultaneously, and the learner switches among (the current learning units of) the learning threads. The learning-path approach is adequate for supporting the development of learning threads on a coarse level of granularity, such as planning the sequences of topics to study. But for learning that occurs on a fine level of granularity, the learning-path approach may not work so well. In this paper, we introduce the concept of curricular automata, and show how this formalism can be used to support both single-thread learning and multi-thread learning.