This study examines the perceptions of Jordanian science teachers' conceptions of assessment, and how these perceptions are affected by the teacher's gender, length of experience, and subject variables. The teacher conception of the assessment questionnaire was completed by 488 teachers. It consisted of 27 items spread over four dimensions: school accountability, student accountability, assessment improves education, and assessment is irrelevant. Results showed a high mean for assessment being irrelevant, followed by assessment improving education, student accountability, and school accountability. The results also showed significant differences in the teachers' perception of school accountability by gender, as the female teachers' mean score was higher than that of the males. There were significant differences in the perception of assessment that improves education, again by the teacher's gender, with female teachers scoring higher. The results showed no significant differences in the perception of any of the dimensions according to the length of teaching experience. Finally, there were significant differences in perceptions of assessment in student accountability according to the subject, the mean score for physics teachers being higher than that for chemistry and biology teachers. Perceptions of assessment improving education and assessment being irrelevant, also varied according to the subject, the mean score for mathematics teachers being higher than that of the chemistry, biology, and physics teachers.