The work reported in this paper reflects a collaborative effort of many individuals representing multiple organizations. It began during a session at the October 2008 meeting of TILSA when a representative of a member state asked the group if any of their programs had experienced unexpected fluctuations in the annual state assessment scores, and if so, whether they have a reasonable explanation for such instability in the scores. Gary Phillips, representing AIR, offered that he had been investigating what he called "score drift" and did have a hypothesis about this phenomenon and offered a brief explanation regarding what he characterized as two unrecognized sources of error that underlie such fluctuations. A panel of nationally recognized experts recently reviewed research conducted by Gary Phillips of the American Institutes for Research on potential causes of the seemingly random fluctuations seen in many annual state test scores--fluctuations that both the state agency personnel and testing vendors often find difficult to explain. Phillips has identified and investigated the impact of two underlying sources of error that contribute to the instability of these annual scores: (1) Sampling error variance associated with cluster sampling of students (referred to as "design effects") rather than true random sampling; and (2) Error variance associated with equating test forms. The purpose of this paper is to summarize the points of consensus reached by the expert panel regarding Phillips' work on methodological factors that contribute to score drift, and the actions state agency personnel can and should take to manage and minimize these sources of error. Appended are: (1) Peer Review Panelists; and (2) Content of the "Score Drift and Design Effects: Why Test Results Bounce up and Down from Year to Year in Some State, District and School Testing Programs." (Contains 3 tables and 4 footnotes.)