Background:  The ability of undergraduate medical sciences students to self-assess is a critical skill, which all health professionals must master. Aim: The aim of this study was to compare the students' self-grading versus tutors' grades and to assess inter-examiner grade variation in preclinical crown preparations of plastic teeth. Materials and Methods: A cross sectional study among fifty 4th-year undergraduate dental students, at semester 7 (2014-2015), at the University of Medical Sciences and Technology, Sudan; and two tutors from the department of restorative dentistry with differing years of experience. Each student prepared a crown of porcelain fused to metal on a plastic molar. After one week students were asked to rate their preparation using the “glance-and-grade” marking system, out of 20 marks. The two examiners also assessed the preparation separately by the same method. A comparison between different variables was done by paired sample t-test and Person’s correlation test with the level of significance set at p-value≤0.05. Results: The mean of students self-grading (13.4±3.37) of the prepared teeth was higher than the mean grades (12.0±3.67) of the junior tutor (p=0.007) and moderate correlation (0.376). The mean of students self-grading is much higher than the mean grades (9.64±3.37) by the senior tutor (p=0.001) and with moderate correlation (0.450). Comparison between the grades means of the prepared teeth by the two tutors revealed statistical significant different (p=0.000) and strong correlation (0.647). The overall mean grades (10.82±5.25) by the two tutors and self-grading (13.40±3.375) by the students were statistically significantly different (p=0.00). Conclusion: Students tended to grade their preparations of porcelain fused to metal crowns on plastic teeth higher than tutors. Inter examiner variation in grading were observed between the junior and senior tutors. Training students in self-assessment methods and the setting of criteria by the faculty is recommended.