The methodology proposed aims to detect the linguistic and cognitive strategies which can help predict “school-efficiency” in students wishing to attend a conference interpreting course. This paper does not enter into the details of the empirical and procedural part of the test. The aim of this paper is to explain the theoretical framework for choosing an oral paraphrasing exercise as a diagnostic tool for aptitude to interpreting. The model to analyse students’ oral paraphrases at three levels, i.e. syntax, semantics and pragmatics will also be discussed. The paper is divided into two parts. The first part presents an overview of aptitude criteria and test implemented world-wide and tackles the issue of the need for an objective measurement of abilities. The second part focuses on paraphrase and our analytical three-tier model and categories.