What Are They Thinking?: Eliciting Student Reasoning About Troublesome Concepts in Introductory Computer Science

Understanding student conceptions and identifying student misconceptions is an important precursor to developing high quality pedagogical materials and approaches. We conducted a pencil-and-paper survey consisting of a demographic questionnaire and 21 content-based questions with 106 students at the start of a second semester course for CS majors (i.e., CS2) at a large public U.S. university with a focus on engineering and science. We then selected the questions that appeared to be most problematic for students and several closely related questions and analyzed the student reasoning for each question and across questions with similar concepts. We found that students exhibited misconceptions related to pass by value versus pass by reference semantics, "false sharing" of variables of the same name in different scopes, and believing that global variables may not be accessed from the main function and/or that a global variable may be modified via a local variable of the same name (i.e., in the presence of variable shadowing). Potential explanations for these misconceptions include fragile knowledge, lack of attention to detail, over-attention to newly acquired knowledge, information foraging (abductive reasoning) in the presence of misleading contextual clues, and lack of exposure to the use of global variables beyond the specification of constants.