In Japan, the focus of English education in both junior high and high schools has generally been grammar instruction. It seems meaningful, given the significant linguistic distance between English and Japanese. However, it is also important to make sure that grammatical knowledge is transferred into practical English production effectively. Nonetheless, there have been few experimental studies on the relationship between grammatical knowledge and production. This indicates that it is highly relevant to examine how grammatical knowledge affects English production at universities in Japan. This study used a quantitative analysis, structural equation modeling (SEM), to investigate the extent of influence of local accuracy (grammatical accuracy in a sentence) on global accuracy (comprehensibility of a sentence and of an essay as a whole). Items for analysis included 155 argumentative essays written on one of two recent social topics. Japanese English professionals evaluated the essays for local accuracy while native English teachers evaluated them for global accuracy. The result indicated a low relationship between local accuracy and global accuracy. Consequently, this study classified the essays into two groups; one with low accuracy and high global accuracy, and the other with high local accuracy and low global accuracy. The causes for the phenomenon were then explored, and practical strategies for the future were discussed including those on evaluation criteria and feedback