Alberto Speaks Italian with His Grandmother and English with Everyone

Alberto speaks Italian with his grandmother and English with everyone else at home, but he is starting school and needs to use English at school. Based on research about bilingualism, what should Alberto be encouraged to do about developing skills in both languages?

A) Develop English only. Bilingual students tend to use code-switching, an indication of low-level language skills.
B) Speak English only. Avoid speaking Italian. The dual languages will interfere with his ability to read and write English correctly
C) Focus on developing English and teach his grandmother to speak English
D) Keep developing skills in both languages. Being bilingual increases cognitive abilities