This article presents information on 2 international educational effectiveness studies, one completed and the other ongoing. The 2nd study is, to a large degree, a reaction to a methodological problem encountered in the 1st study, the lack of an internationally valid instrument measuring teacher effectiveness. This article presents 4 reasons for conducting the 2nd study (International System for Teacher Observation and Feedback (ISTOF)) and then details the overall work plan for ISTOF-I (2004-2006) and ISTOF-II (2006-2007). The sample of 20 fully participating country teams in ISTOF is very diverse with representatives from nearly all geographic areas of the world (North and South America, Europe, Africa, Asia), many of which have never participated in teacher or school effectiveness research. This article summarizes progress made on the development of the ISTOF protocol, including the generation of components and indicators of teacher effectiveness. In many ways, the study is already a success, due to the diversity of the participating countries and their generation of major parts of the protocol during ISTOF-I. Nevertheless, this article concludes with a discussion of some of the major challenges that the research team will face as it begins ISTOF-II. (Contains 4 tables and 6 notes.)