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 proceeds to use this framework to identify potential sources of invalidity in the test being examined, and concludes that a