This paper describes several methodological decisions made during a study of linguistic development of French in British classroom learners, highlighting the significance of choosing suitable tools for collecting, transcribing, and analyzing oral interlanguage data and noting the usefulness for interlanguage research of the CHILDES (Child Language Data Exchange System) procedures, which consists of three integrated components: the Talkbank database, CHAT (Codes for Human Analysis of Transcripts), and CLAN (Computerized Language Analysis). This paper is based on the Linguistic Development in Classroom Learners of French research project, which documents linguistic progression among classroom learners of French in grades 9-11, analyzes the development of morphosyntactic structures in spoken learner French, and evaluates the creative construction process and its interaction with formulaic languages among instructed learners. The paper notes general problems with the transcription and coding of French interlanguage but suggests that experiences to date with using CHILDES is encouraging. Three appendixes include elicitation tasks, CHAT symbols, and examples of preliminary transcription. (Contains 14 references.) (SM)