What do "CS1" and "CS2" mean? Investigating differences in the early courses

Thirty-one years ago, the ACM Computing Curricula used the terms "CS1" and "CS2" to designate the first two two courses in the introductory sequence of a computer science major. While computer science education has greatly changed since that time, we still refer to introduction to programming courses as CS1 and basic data structures courses as CS2. This common shorthand is then used to enable students to transfer between institutions and as a base of many research studies. In this paper we show that while there is wide agreement on the connotation of CS1 and CS2, there is little agreement as to the denotation of these terms. Surveying CS1 and CS2 instructors, we find little agreement on how important various topics are to each of these course and less agreement on how well students master the material. Even after limiting the analysis to whether a topic has ANY important or students complete a course with ANY mastery of the material, we continue to find significant disagreements between instructors.