Mode estimation, the visual determination of the proportions of the components of a rock, is a valuable tool in geology, providing one of the most efficient means of describing rock mineralogy and chemistry. However, current methods of teaching mode estimation suffer from the often-mediocre mode-estimation skills of the instructors. Fifty-nine academic and professional geologists was surveyed online to assess their mode estimation skills, and they scored 65.9 ± 7.5 (SD) out of a possible 100. Instructors with poor skills cannot provide the correct answers to mode questions and, thus, cannot create valid assessments of student mode-estimation skills. Two computer programs may help address this problem. ModeMaker is a tool for the instructor to use to create images with up to five phases, each with known modes. Each phase can have a number of additional specified properties, such as shape, size, and orientation. The instructor can, thus, provide valid assessments of student abilities to estimate modes. ModeQuiz is an interactive training application for the student. It creates images of the sort ModeMaker creates but randomizes the properties. The student makes mode estimations on the computer, and the program reveals the correct modes and scores the student's estimates. By repeating this process, the student may improve his or her mode-estimation skill over time. Assessments of ModeQuiz show that as little as 2 h of practice with the program may lead to improvement in student skill at mode estimation.