The process oriented approach to English-as-a-Second-Language (ESL) instruction has spurred such new ideas as student instruction and the whole language approach. New thinking justifies the validity of qualitative research, which lets researchers view subjects' learning processes from previously impossible angles. This paper examines ESL writing expertise and English language proficiency. It explains that how students plan, organize, revise, and edit their writing is as important as their English language proficiency. Conventional methods of grading and correcting students' compositions are inadequate, because they rely too heavily on language proficiency. When writing, language interacts with writing expertise. Correcting grammatical and word errors seem to be a constant focus for Taiwanese ESL students and teachers, though many instructors try to teach how to organize ideas or write a topic sentence. What students put down on paper is a combination of both writing expertise and English proficiency. ESL writing teachers must find clues that indicate, in terms of writing expertise and English proficiency, what kinds of strengths and weaknesses each student has. ESL writing instruction is most effective when teachers see through flawed language and understand what kind of help each student requires. (Contains 40 references.) (SM)