This article introduces a dedicated, computer-supported method to construct and formatively assess open, annotated concept maps of Personal Professional Theories (PPTs). These theories are internalised, personal bodies of formal and practical knowledge, values, norms and convictions that professionals use as a reference to interpret and acquire knowledge, and to direct their behaviour, and which vocational students are expected to develop. Monitoring the development of PPTs and assessing their quality are difficult as they are, essentially, mental schemes. Traditional methods, such as semi-structured interviews and concept mapping, are either too labour-intensive to be used in an educational setting or are not able to reveal their full quality. The study presents a new method which is valid, reliable and easy to use in education and which reveals the quality in a way that is comparable to or better than interviews.