This research investigated the similarities and differences between Korean and U.S. 9-12th grade science classrooms. The Reformed Teaching Observation Protocol was used to observe sixty-six classrooms (26 Korean and 40 U.S.) to examine the extent to which principles of constructivism framing both Korean and U.S. standards documents were observed. Through quantitative methods the findings revealed generally more similarities than differences when comparing Korean and U.S. classrooms. This was evidenced by the lack of overall significant differences in how the classrooms were rated, as well as the lack of overall significant differences in each subscale of reformed teaching measured by the RTOP ("Lesson Design, Content & Process, & Classroom Culture"). But, "Student and Teacher Relations," one of the two subscales of Classroom Culture in the RTOP was found to be different with U.S. teachers rated significantly higher than the Korean teachers. Our findings have led us to conclude that there is still significant room for improvement in both Korea and the U.S. in aligning student experiences in science classrooms with those visions outlined by reform efforts framed by principles of constructivism. (Contains 4 tables and 3 figures.)