Pienmann (1998; 2011) has proposed an L2 developmental schedule known as his “Processability Theory” or PT. The theory has been assumed in many empirical studies using not only speaking tasks (production) but reception tasks. However, writing studies for PT have not yet been developed. In this study, Mihimoto’s two empirical studies (Michimoto, 2015a; 2015b) are used in order to examine PT through writing tasks and to establish a suitable method for designing writing tasks. Important technical issues which need to be overcome are discussed. The present study considers how, based on PT, to handle communicative writing tasks under time controls. Another issues discussed is how to recognize language chunks and how to deal with them. In addition, the possibility of incompatibility with PT developmental stages is shown.