We investigated how 2 different curricular scaffolds (context-specific vs. generic), teacher instructional practices, and the interaction between these 2 types of support influenced students' learning of science content and their ability to write scientific arguments to explain phenomena. The context-specific scaffolds provided students with hints about the task and what content knowledge to use in or incorporate into their writing. The generic scaffolds supported students in understanding a general framework (i.e., claim, evidence, and reasoning) regardless of the content area or task. This study focused on an 8-week middle school chemistry curriculum that was enacted by 6 teachers with 578 students during the 2004-2005 school year. Analyses of identical pre- and posttests as well as videotapes of teacher enactments revealed that the curricular scaffolds and teacher instructional practices were "synergistic" in that the effect of the written curricular scaffolds depended on the teacher's enactment of the curriculum. The context-specific curricular scaffolds were more successful in supporting students in writing scientific arguments to explain phenomena, but only when teachers' enactments provided explicit domain-general support for the claim, evidence, and reasoning framework, suggesting the importance of both types of support in successful learning environments. (Contains 4 tables, 6 figures, and 7 footnotes.)