The ability to solve problems is a key skill and is essential to our day-to-day lives, at home, at school and at work. The present study explores the quality of managerial problem-solving of participants who are in secondary education. We studied 10th, 11th, and 12th graders following a business track in the Netherlands. Participants were asked to represent, diagnose and solve business cases. The transcripts (handwritten "case solutions") of all 213 participants were analysed for managerial knowledge and problem-solving accuracy. Futhermore, we controlled the data for individual interest. The results demonstrate students' progress in terms of the quality of solving problem from 10th grade until 12th grade. Several implications for education are discussed.