此個案研究旨在檢視一雙語家庭中， 非以英語為母語之雙親遵循【一人一語言】(one-person-one-language)之言談策略與其兩歲女童使用中、英語言轉換之關係。經為期一年之每月觀察親子互動記錄顯示：女童父親使用中文與其互動時，較容許女童雙使用中、英夾雜，且不堅持女童需使用中文與其互動；但女童母親則要求女童以英語與其互動。因此，女童使用中文或中、英夾雜方式與父親互動，與母親互動時，則多使用英文，較少中、英夾雜。一系列相關統計分析顯示：女童雙親因應女童中、英夾雜使用不同言談策略，而雙親不同之言談策略，與女童後續使用中、英夾雜之頻率，多呈正向顯著相關。證據亦顯示：女童在與雙親互動時，似習得不同語用知識，在觀察後期中，女童能明確說出家中【一人一語言】之模式，並糾正母親應使用英文與其互動。本研究之貢獻在於使用【質量混合】之研究方法，為【雙親言談策略假設】提供部份佐證。

The case study was conducted to examine the relationship between parental discourse strategies and the mixed-coding of language behavior of a 2-year-old Mandarin-English bilingual girl in interactions between the parents and the child. The parents were non-English native speakers and adopted the one-person one-language practice in the family, where the father spoke Chinese to the daughter and allowed the daughter to respond in either Chinese or English, while the mother used only English in the interaction with the daughter. Monthly recordings of the child's naturalistic interactions with both parents over one year revealed that the father was more tolerant of the child's mixed coding, and the mother was intolerant. The child used mixed Mandarin and English in interactions with her father frequently, but less frequently used the mixed coding with her mother. A series of correlation analyses shows that parents' discourse strategies in response to the child's mixed coding of language are positively and significantly correlated with the child's overall rates of using mixed-coding and the likelihood that the mixed-coding was used in the next round of conversation. It seems the child differentiated pragmatic strategies in her interactions with respective parents. She recognized the one-person-one-language rule in her interactions with her mother and eventually appliedit in her interactions with her father. The significance of findings of the study is to contribute partial empirical support for Parental Discourse Hypothesis through a mixed methodology.