Spreadsheets are arguably the most widely used programming language in use today, yet spreadsheets commonly contain errors. Research shows that regardless of the experience of the end user, an alarming number of spreadsheets contain errors (91% in recent field audits). Most spreadsheets are created by end users with little or no programming experience. Unfortunately, software engineering research has largely ignored these users. In an attempt to reduce this high error rate, our research is aimed at bringing the benefits of software engineering to end users without requiring that they first learn software engineering principles. One mechanism for creating error-free programs is assertions. An assertion is a program property that always holds. It provides a way to attach more of the specification to the program. We have developed an assertion tool for spreadsheet languages that extends Microsoft Excel's validation scheme and includes capabilities such as assertion propagation. This work describes an empirical study done to assess how well end users understand and use the information provided by the assertion tool as they perform maintenance tasks. The study also provides information about end users' testing behavior. / Graduation date: 2002