The main purpose of this chapter is to discuss briefly major methodologies used for the analysis of change. Throughout the development and maturation of approaches to measuring change, different types of change have been recognized and different methods of quantifying change have been developed (e.g., Collins and Horn 1991; Harris 1963). There is a colloquial reference to so-called old and new approaches to measuring change. ‘Old’ approaches refer to such conventional indicators of change as the differences between measures in a given time point and a subsequent time point. ‘New’ approaches refer to ever more complex methodologies for describing and quantifying development, whether spontaneous or occurring in response to intervention.

Clearly, the amount of information on a subject studied by many outstanding scientists that can be introduced in a single chapter is limited. Moreover, a single chapter cannot compete with the comprehensive volumes that have recently been written on the same topic (e.g. Collins and Sayer 2001; Gottman 1995; Moskowitz and Hershberger 2002; von Eye and Niedermeier 1999). Therefore, the strategy selected in this chapter for material presentation is to introduce briefly selected methodological approaches, illustrate them with specific examples, and provide the reader with a wealth of relevant references.

We decided to illustrate various change-related methodologies by reviewing a limited content area – the field of studies related to acquisition, both natural and in response to targeted intervention, of oral and written language. Such a decision is not random, of course. The selection was driven by two considerations.