This article focuses on the capacity of students to develop and assess argu
ments during a high school genetics instructional sequence. The research fo
cused on the locating distinction in argumentation discourse between "doing
science" vs. "doing school" or "doing the lesson" (Bloome, Pure, & Theodor
ou, 1989). Participants in this classroom case study were high school (9th
grade) students in Galicia (Spain). Students were observed, videotaped, and
audiotaped while working in groups over six class sessions. Toulmin's argu
ment pattern was used as a tool for the analysis of students' conversation
and other frames were used for analyzing other dimensions of students' dial
ogue; (e.g., epistemic operations, use of analogies, appeal to consistency,
and causal relations). Instances of "doing science" and instances of "doin
g the lesson" are identified and discussed as moments when the classroom di
scourse is dominated either by talking science or displaying the roles of s
tudents. The different arguments constructed and co-constructed by students
, the elements of the arguments, and the sequence are also discussed, showi
ng a dominance of claims and a lesser frequence of justifications or warran
ts. Implications for developing effective contexts to promote argumentation
and science dialogue in the classroom are discussed. (C) 2000 John Wiley &
Sons, Inc.