當母語者與非母語者在進行溝通時，母語者通常會使用較為簡化的語言形式，此種語言形式研究者稱之為「調整語」。本文旨在探討在台灣的成人美語教室中，外籍教師針對不同程度的學生，使用調整語的情形，文中主要從「句法」與「言談功能」兩個角度分析外籍教師的語言使用。
有三位教授中、高級美語會話的外籍教師參與本研究，每位教師於不同層級的課堂各接受兩次錄音，總計收集到18小時的錄音語料，351頁的逐字稿，全數經過分析比較後，主要發現如下：
(1) 外籍教師之語言平均句長並未隨著學生程度越高而有顯著增加。外籍教師在中級教室之平均句長為8.197，在高級教室為8.388，p>0.05。此結果顯示，當學生程度到達中級以上，「句長上的調整」似乎不再是外籍教師採用的調整方式。
(2) 外籍教師之語法正確率在兩個層級都非常高。外籍教師在中級教室之語法正確率為99.81%，在高級教室為99.79%，在兩個層級都僅有10個錯誤句子，透過錯誤類型分析，發現中級教室中出現較多句法層面上的錯誤，而篇章層面的錯誤則全出現在高級教室中。
(3) 外籍教師之言談功能會隨學生層級不同而有調整。外籍教師在中級教室中給予較多主動的語言輸入、提供較多的發問，主要功能為傳輸語言知識；在高級教室中，教師減低發言的比例，使用較多的回饋功能。
綜合以上研究結果發現，英語為母語之外籍教師在上課時面臨不同語言程度的非母語對話者有不同的語言調整方式，在中、高級程度的班級上，「句法上的調整」不再是外籍教師的主要考量，而轉向採用「語言功能上的調整」，在教學應用上，儘管隨著學生層級的增加，外籍教師減少了「主動語言輸入」功能，而採用較多的「語言回饋」功能，但整體而言，學生發言的比例仍然偏低（中級教室9.93%；高級教室12.15%），教師應給予學生更多的口語練習機會，採用更多的回饋機制，以增加學生之溝通能力。

When addressing to non-native speaker, native speakers will modify his speech to what he thinks is simpler and easier for the non-native listener to comprehend. Such simplified register is referred to as “Foreigner Talk.” The present study aims to explore both the syntactic and discourse characteristics of FT in Taiwan’s adult English classrooms. Three measurements (1) syntactic complexity (2) grammaticality and (3) discourse functions are adopted to investigate if the interlocutor’s language proficiency affects the foreigner teacher’s language use. The data were collected from 18-hour recording of three English native speakers’ utterances in intermediate and advanced classrooms. The major findings of this study are summarized as follows:
(1) In terms of syntactic complexity, the mean words per t-unit at both levels are very similar with 8.197 at the intermediate level, and 8.388 at the advanced level. The result of t-test (p>0.05) also indicates that no significant difference is found concerning the language complexity between the two levels. It is suggested that the adjustment of language complexity may only resort to students with lower proficiency. Once the student’s proficiency goes beyond a specific level, the length of teacher’s utterances will keep in a fixed range.
(2) In terms of grammaticality, over 99.79% of the foreigners’ utterances are grammatical sentences in both language classrooms, showing that the foreigners’ language form is quite accurate. By analyzing the 20 ungrammatical utterances, it reveals that the foreigner teachers are more likely to utilize the syntactic adjustment for the lower level learners and conserve the discourse adjustment for the more advanced ones.
(3) In terms of discourse functions, Sinclair and Coulthard’s model (1992) is modified to categorize the functions of the foreigners’ utterances. It is found that the distribution of the functions varies with the development of the students’ language ability. The foreigner teachers use significantly more initiation functions to the intermediate students and provide much more responsive functions for the advanced students.
Based on the findings of this study, some pedagogical implications are addressed. It is suggested that teachers should pay more attention to their language use and consider if their adjustments of language really enhance language learning. In order to increase the learning potential, teachers are recommended to employ more judicious silence, to reduce the percentage of teacher-initiated utterances and to resist the temptation to interrupt. Also, teachers should realize that they are not only an instructor but also an interlocutor for their students at the same time. By realizing the dual roles as being a language teacher, the teacher can make language class less artificial and help learners to overcome the gap between communication in and outside the classroom.

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