In this paper we analyze the CS Principles project, a proposed Advanced Placement course, by focusing on the second pilot that took place in 2011-2012. In a previous publication the first pilot of the course was explained, but not in a context related to relevant educational research and philosophy. In this paper we analyze the content and the pedagogical approaches used in the second pilot of the project. We include information about the third pilot being conducted in 2012-2013 and the portfolio exam that is part of that pilot. Both the second and third pilots provide evidence that the CS Principles course is succeeding in changing how computer science is taught and to whom it is taught.

Let P be a set of n points in the plane. The Yao graph for P is a geometric graph obtained by extending equally spaced rays from each point u ∊ P, and connecting u to a closest neighbor in each sector formed by these rays. Associated to this graph is an integer parameter k > 1 defining the number of rays. The out-degree of the Yao graph is k, but the in-degree can be as large as n − 1. To overcome the problem of potential high in-degree, the Sparse-Yao graph (also known as Yao-Yao graph) eliminates from the Yao graph all but a shortest incoming edge in each sector. It has been established that the Yao graph defined by integer parameter k ≥ 6 is a t-spanner, for some real constant t > 1, meaning that it has a path between each pair of points in P of length at most t times the Euclidean distance between the two points. The constant t is called the stretch factor of the Yao graph. The problem of determining whether the Sparse-Yao graph is a spanner or not has been long open. In this paper we make progress on this problem by showing that the Sparse-Yao graph defined by integer parameter 6k, with k ≥ 6, is a spanner with stretch factor 11.67. With parameter k ≥ 8, the stretch factor drops to 4.75.