Importing design patterns from software engineering to the computer science education (CSE) field was followed by defining patterns and pattern languages suitable for CS courses. The main goal of incorporating patterns in CSE was to enhance students' programming abilities, as well as their design and problem-solving skills. Accordingly, various instructional materials were suggested for using patterns in classroom learning activities, such as collections of patterns and related programming assignments. However, the existing pattern-based materials seem to be insufficient for implementation in the classroom, especially when teaching introductory courses that emphasize syntax and programming language features. Therefore, alternative methods using applicative models for pattern-based instruction, which emphasize problem solving and program design issues rather than specific language features and syntax, should be developed and assimilated within the CS teaching community. We believe that successful implementation of such models should be accompanied by appropriate teachertraining.In this paper we describe an initial effort to expose CS teachers to the notions of pedagogical patterns and pattern-based instruction, aimed at motivating them to meaningfully adopt and adapt patterns to their concrete pedagogical needs.

Recursion is a central concept in computer science, yet it is a very difficult concept for beginners to learn. In this paper we focus on a specific aspect of comprehending recursion -the conception of the base case as an integral component of a recursive algorithm. We found that students have difficulties in identifying base cases: they handle redundant base cases; ignore boundary values and degenerated cases; avoid out-of-range values; and may even not define any base cases when formulating recursive algorithms. We also found that students have difficulties in evaluating recursive algorithms that deal with imperceptible base cases. We suggest that teachers should make a special effort to discuss different aspects of the base case concept. Emphasis should be put on both declarative and procedural aspects of categorizing and handling base cases as part of recursion formulation.

The notion of an algorithm is fundamental in computer science. Yet, it is not always fully conceived by novices. This paper focuses on a particular facet of algorithm conception -the relationship between an algorithmic problem, its analysis, and its desired algorithmic solution. The paper displays evidence that novices demonstrate cognitive obstacles regarding the notion of an algorithm, which relate to a process-object duality phenomena [13] and inadequate classroom norms of communication.