The purpose of this study is to elaborate Michimoto’s analysis (2015a) regarding testing as to whether Processability Theory (PT) can predict developmental stages with writing tasks. PT validity has been supported by a number of empirical studies concerning speaking (e.g. Kawaguchi, 2009; Spinner, 2011; Baten, 2011). On the other hand, Håkansson and Norby (2006) studied Swedish learners’ writing performance. However, they did not use tasks to elicit spontaneous production according to PT. The other writing PT study is Michimoto (2015a). 45 Japanese EFL learners participated in the study. However, the results did not provide evidence consistent with PT. In the current study, a reanalysis was done for the data from Michimoto (2015a) by separating morphology and syntax in accordance with recent PT studies (Yamaguchi and Kawaguchi, 2014; Eguchi and Sugiura, 2015). The results of writing done by the subjects show evidence of predictive ability regarding learners’ syntactic structures based on PT.