The study investigates whether different English learning contexts result in different grammar development in learners’ shared mother tongue, Korean. The research instrument included a sentence completion task of collocational expressions in Korean dialogues, a multiple-choice test of grammar in Korean sentences and dialogues, and a sentence composition task using double nominative structures. The participants were 26 students at the age of 8 to 9 year old in the EFL context, 21 in a type of immersion program, and 19 in the ESL context. The results showed little difference among the three groups in the collocation sentence completion task and the multiple-choice test, but a clearly significant difference between the EFL students and the ESL students in the double nominative sentence composition task. The students who had been learning English in English culture showed more limited knowledge in the writing sentences with such peculiar but common structures in Korean language, compared with those who had been learning English in a Korean cultural context. In the complementary correlation analysis of the scores in the sentence composition task with a double nominative structure, the length of residence in Korea proved the strongest correlation, implying that the longer students live in Korea, the better they perform. The study provides the pedagogical implication that the curriculum of a mother tongue for bilingual learners could need to intervene with more emphasis on enhancing learners’ grammatical development, including language-specific structures.