The present study reports the process of development and validation of a rating scale in the Iranian EFL academic writing assessment context. To achieve this goal, the study was conducted in three distinct phases. Early in the study, the researcher interviewed a number of raters in different universities. Next, a questionnaire was developed based on the results of the interview along with the related literature. Later, the questionnaire was sent to thirty experienced raters from ten major state universities in Iran. Results of the country-wide survey in this phase showed that there was no objective scale in use by the raters in the context. Therefore, in the second development phase of the study, fifteen of the raters who participated in the first phase were asked to verbalize their thoughts when each rating five essays. At the end of this phase, a first draft of the scale was developed. Finally, in the last validation phase of the study, ten raters were asked to each rate a body of twenty essays using the newly developed scale. Next, eight of the raters participated in a follow-up retrospective interview. The analysis of the raters' performance using FACETS showed high profile of reliability and validity for the new scale. In addition, while the qualitative findings of the interviews counted some problems with the structure of the scale, on the whole, the findings showed that the introduction of the scale was well-received by the raters. The pedagogical implications of the study will be discussed. In addition, the study calls for further validation of the scale in the context.