Chapter 11 examines what evaluation studies tell us about the effectiveness of TBLT. These studies are practice oriented, addressing whether TBLT ‘works’ and what might be done to make it work more effectively. The chapter begins with a discussion of TBLT as an innovation and illustrates how the factors that affect the success of educational innovations in general can predict and explain the success or failure of particular TBLT programmes. The chapter then reviews a number of actual evaluations – both macro-evaluations of complete TBLT programmes and micro-evaluations carried out by teachers implementing specific tasks in their own classrooms. Drawing on these evaluations, the chapter ends with a discussion of the major problems that teachers face in implementing TBLT and suggests some solutions.