The use of standard-based assessment, grading and reporting tools is essential to ensure that assessment meets acceptable levels of quality and standardization. This study reports the design, development and evaluation of a standards-based assessment tool for the instructors at Sultan Qaboos University, Sultanate of Oman. The Rapid Applications Development Model was implemented to develop early versions of the assessment tool, called RealGrade. The Grading tool Usability Questionnaire and a series of individual interviews were used to measure participants' reactions toward the usability of RealGrade and determine the extent to which the prototype is usable. The results revealed that participants found the RealGrade effective and efficient in facilitating the process of standardsbased assessment and communicating grades with students at the University. In addition, they favored the design, flexibility and ease of use of RealGrade. Further examinations of mean differences among participants according to their computer experience and teaching experience were conducted.