At this juncture, it is hoped that I have clearly demonstrated that the proposed integrated approach to theorizing and measuring the WM construct not only provides perceivable theoretical advantages, but also has significant implications for practical research on L2 acquisition, processing and performance. In this chapter, I extend the integrated perspective to demonstrate its implications for L2 development within the broader context of L2 aptitude research. To that end, I argue that WM should be included as a central component of L2 aptitude. To achieve this goal, the chapter is divided into four sections. The first section provides a critical review of the major L2 aptitude models, ranging from Carroll's four-factor model to more recent models that aim to reconceptualize Carroll's original concept. The following section makes a formal case for incorporating WM into L2 aptitude and outlines the perceivable advantages and limitations of this proposal. In the third section I propose a number of directions for future aptitude research, which should ultimately lead to a reconfiguration of language aptitude within SLA. The summary section concludes the chapter.

A Critical Review of the Current Language Aptitude Models

No review of L2 aptitude research can afford to bypass the American psychologist John Carroll and his early work conducted during the 1950s and 1960s (Wen & Skehan, 2011). Carroll broke the shackles of the earlier prognosis tests and spearheaded research on L2 aptitude (Spolsky, 1995). To a large extent, his early contributions to L2 aptitude served as a blueprint for later research efforts. First, the Modern Language Aptitude Test (MLAT) battery developed by Carroll and his colleague Stanley Sapon (Carroll & Sapon, 1959/2002) laid the foundation for all subsequent aptitude measures (e.g. Pimsleur’s Language Aptitude Battery, Green’s York Language Aptitude Test, Petersen and Al-Haik’s Defense Language Aptitude Battery and Parry and Child’s VORD).