knowledge as context for skills

Traditional models of assessment have tended to focus on the testing of understanding and ability to apply knowledge. That knowledge changes over time but the method of assessment is fundamentally the same as it has been since the introduction of public examinations. When the teachers are asked what makes a good mathematician or what makes a good historian they don't say it is someone who can do calculus or someone who knows about the Romans. These and other subjects have a set of skills which underpin the knowledge. Essentially the knowledge is the context for these skills to be applied. It seems strange then that we only assess the knowledge and focus little on assessing the skills which underpin this knowledge and therefore do not directly support the development of these skills.