Most teacher education assessments are criticized for lacking validity and reliability. This study describes the process of developing the Observation of Field Performance rubric to assess initial teacher candidates' classroom performance and establishing the content validity as well as reliability of the rubric. A panel of content area experts determined that 10 out of 12 items of the rubric were essential and the CVR was above the acceptable range for all 12 items, indicating that the rubric had a strong content validity. Additionally, the analysis of instructors' ratings on the rubric showed that the rubric had good level of internal consistency and inter-rater reliability. Thus, this study determined that the OFP is a reliable and valid measure of candidate performance during field practice. Establishing validity and reliability not only enables teacher education programs to collect high quality assessment data, it is also crucial for program approval and accreditation decisions by national and state agencies.