The present study aims at pursuing Japanese junior high school students' knowledge about English noun phrase structures and the process of its development based on the data collected longitudinally. About 160 students had joined in this study for 3 years (from 2006 to 2009). The participants took eight grammar tests consisted of questions about: 1) noun phrases with premodification by adjectives, 2) noun phrases with premodification by interrogatives, 3) noun phrases with postmodification by prepositional phrases, and 4) noun phrases with postmodification by to infinitive phrases. The questions were divided into mainly two categories: 1) that is to test whether students know the correct word orders in the target noun phrases, and 2) that is to test whether they could identify the target set of noun phrases in sentences. We also investigated if the knowledge of noun phrase structures could discriminate those who succeeded in their English language study from those who did not. The obtained results showed that a fairly long period of time was needed for learners to acquire the structures and the difficulties of acquisition varied from noun phrases and also from question types. It is also revealed that the discriminative power of the noun phrase knowledge is strong enough.
