Students often come to a principles course in economics with knowledge that is not correct. This example asks students to guess the percent of federal expenditures for different spending categories. They are then shown the actual percentages. The student results can be the source of a class discussion on why many of their initial estimates were wrong (as they generally are). Students can also create their own budget by changing the amounts spent in each category. Budget Explorer, implemented over the internet, uses data from the Public Budget Database of the White House Office of Management and Budget.