The Problem Decomposition Diagnostic is a testing instrument designed to help determine student ability in two areas of problem solving. As the name implies, all versions of the test have been intended to gauge student ability to decompose, or break up, complex physics problems into simpler sub-problems. Additionally, later versions of the PDD sought to also examine the strategy the student would use to solve such subproblems.

This thesis is organized in a roughly chronological manner, following the development of the Problem Decomposition Diagnostic from early open response tests and interview tasks to the current multiple-choice format instrument. Both qualitative and quantitative methods were used in developing this instrument and measuring its validity. Extensive appendices include every version of the test, plus a complete laboratory course which helped inspire this work and informed a number of the aspects of the PDD.