Morphological competence plays an important role in extending one’s vocabulary in grammatical context. This study is to explore the developmental distribution of English grammatical morphemes appearing in elementary English textbooks. To this end, the study developed grammatical morpheme recognition and elicitation tests based on the bilingual syntax measurement (BSM). The tests are given to 114 fifth graders and 126 sixth graders across small, medium and metropolitan cities. The students were stratified into high, mid and low English ability groups by their English achievement scores. The result shows that English grammatical morpheme awareness was positively correlated with students’ English ability. The grammatical morphological development of Korean students was more in alignment with that of English learners as a foreign language than that of native speakers. Pedagogical implications are provided at the end of the paper.