To improve mathematics achievement, students' errors should be treated as a source to stimulate their understanding of the conceptual and procedural basis of their errors. The study investigated 20 Chinese and 20 U.S. high school teachers' interpretations and responses to a student's errors in solving a quadratic equation. The teachers' responses were analyzed quantitatively and qualitatively. Analysis results show that the Chinese teachers provided more negative evaluations toward students' errors and identified more students' errors than the U.S. teachers did. Responding to students' errors, the two groups of teachers highlighted conceptual explanations targeting students' mistakes. The U.S. teachers were more likely to provide general knowledge guidance while the Chinese teachers tended to go back to basic knowledge. [For the complete proceedings, see ED583608.]