This study aims to investigate the impact of a training package in laboratory work assessment techniques on science teachers' understanding of these techniques and their perceptions about them. The study sample consisted of (23) science teachers in physics, chemistry, and biology) of the 11th grade in Al-Batina Region (South). This sample formed the experimental study group of which the proposed training package was provided to. The packages based on the assessment techniques of laboratory work, and included information, activities and skills related to them. It was applied for two weeks and one day during the 1st semester of the academic year 2006/2007. To answer the study questions, two instruments were used: 1. Test of Teachers' Understanding of laboratory Work Assessment Techniques. The validity of the test was out through a panel of (9) judges, and the reliability level was found to be (0.82) and was applied before and after the period of the training Package. Teacher Perceptions Scale towards laboratory Work Assessment Techniques. The validity of the scale was out through a panel of (10) judges, and the reliability level was found to be (0.80) and was applied in three periods before the training Package, straight after applying the Package, and after three months of applying the Package. Results of the study showed that in the understanding test of assessment techniques between pre and post-test there was statistical significant difference at the level (a < 0.01) in favour of post-test. This proves the impact of the training package in enhancing the level of the teachers' understanding of these techniques. The study also showed that there is a development in the teachers' perceptions towards laboratory work assessment techniques. This was indicated from the statistical significant difference between the pre-period and 15 post-period perceptions, and also the statistical significant difference between the pre-period and 2nd post-period perceptions. The study did not find any statistical significant difference between the 1st post-period and 2nd post-period perceptions. The study recommends that some of the laboratory work assessment techniques that has been given in the assessment document by the ministry of education should be fully described. Such a description may include observation techniques or lab reports. The study also recommends the importance of applying training packages for the purpose of training teachers to maintain the impact of training for a longer period of time and benefit from the knowledge and skills in this package to the best extent.