Mathematical knowledge for teaching (MKT) measures have been widely adopted by researchers. Critics have debated the value of such measures and questioned the type of knowledge that these access. This article reports on a study where the challenges in measuring teachers' knowledge were illuminated through investigating relationships between the types of knowledge displayed in teachers' responses to a set of MKT items and in their associated constructed responses. The analytical approach implemented is directed content analysis, while cognitive types of teachers' content knowledge are used as theoretical framework. Findings indicate that the teachers' constructed responses do not always support their multiple-choice responses. This research contributes to the overall discussion concerning the challenges of accessing and assessing teachers' knowledge.