This chapter discusses the design and field testing of a computer-based test instrument to assess financial competence. The context for the instrument is decisions to purchase a mobile phone and sign a contract for mobile services within a predetermined budget. The reason for focusing on these decisions is that a significant share of debt has been attributed to telecom services. Since the search for financial information and subsequent purchases or contracts are usually conducted online, our instrument’s scenario is also computerized to simulate an actual purchase. This digital scenario tasks participants with selecting mobile phones and contracts based on specified conditions. They must decide whether to purchase the phone and sign the mobile phone contract separately or bundled, eliminating impractical combinations. The remaining choices are realistic and yield the most favorable option. The scenario concludes with signing the purchasing contract. Subsequent queries ask participants to justify their choices and to rate their motivational activation and interest in the scenario. The chapter describes the process of developing the test items based on scientific models. It presents the results from an initial validation study with more than 100 apprentices who took the test in September 2023. It became clear that some items were too difficult for the apprentices, but on the other hand the test is basically a reliable instrument. While correlations between cognitive and non-cognitive components could be identified, no stronger correlations are found for the analysed dispositions, e.g. mathematics and language ability and personal background such as age.