Spreadsheets have become commonplace, facilitating decision-making at all levels in most organizations. Their ease of use is unfortunately accompanied by an abundance of errors, which some researchers have discovered to reach the magnitude of billions of dollars. There are two main streams of research in this area. One focuses on the categorization of and extent to which errors are made, and the other focuses on detection of those errors. The error detection studies have found that errors are very difficult to detect, and spreadsheet builders fail to plan and test adequately. This study advances that work by testing the relative importance of instructing novices in spreadsheet planning and testing. To date, the data seem to indicate a significant effect of instruction in the planning phase. However, some inadequacies in the data lead us to draw only tentative conclusions, and further testing of this and a future, additional sample will provide a more substantial basis for our conclusions.