This paper examines transformational learning experiences of computing students as a way to better understand threshold concepts in computing. From empirical evidence we found that students often describe transformative experiences as learning situations in which they were led to use various kinds of abstraction, for example modularity, data abstraction, inheritance, polymorphism, reuse, design patterns, and complexity. Some students describe an abstract concept as coming first, and then needing to be made concrete though application; others describe transformations in which they learn the advantages of these abstract concepts from their experience of not using them.

Abstraction is certainly of central importance in computer science. It appears, however, from our students' descriptions of transformative experiences, that abstraction per se is not a threshold, but that particular concepts in which abstraction is paramount exhibit the characteristics of threshold concepts.