This book reports on a two-part study: the validation of a test of spoken English for Norwegian secondary school pupils and the corpus-based investigation of the role played by 'smallwords', such as 'well', 'sort of', and 'you know', in bringing about fluency. The first study builds on the Messickian six central aspects of construct validity to produce a practical framework for test validation. It identifies potential sources of invalidity in the test being examined particularly relating to 'fluency'. The second study sets about to explore the concept of fluency, and to expose the extent to which it is acknowledged in the literature to be associated with smallwords, albeit under other names. The findings from the corpus study are drawn on to propose new elements to include in descriptors of fluency, and the implications of the study for classroom practices are discussed.