The purpose of this paper is to engage with the complexities of describing teachers' professional knowledge and eventually also their learning through written tests. The bigger research aim is to describe what knowledge foundation phase teachers acquired during their two years of study towards the Advanced Certificate of Teaching (ACT). We designed a written test to investigate the professional knowledge that teachers bring with them when they enrol for the ACT, with the aim of comparing their responses to the same test two years later, when they had completed the programme. The questionnaire included questions on teachers' content knowledge; their pedagogical content knowledge (in particular, teachers' knowledge about learner misconceptions, stages of learning, and ways of engaging these in making teaching decisions); and their personal knowledge (such as their beliefs about how children learn and barriers to learning). It spanned the fields of literacy in English and isiZulu, numeracy, and general pedagogy. Eighty-six foundation phase teachers enrolled for the ACT at the University of KwaZulu-Natal completed the questionnaire, and their responses pointed us to further methodological issues. We discuss the assumptions behind the design of the test/ questionnaire, the difficulties in formulating relevant questions, and the problems of 'accessing' specific elements of teacher knowledge through this type of instrument. Our process shows the difficulties both in constructing questions and in coding the responses, in particular concerning the pedagogical content knowledge component for teachers from Grade R to Grade 3.