A test instrument, made up of 25 items, derived from existing standardized tests from literature, was used to probe for the students' knowledge and understanding of basic mechanics concepts, as well as the confidence in the correctness of their answers. The test was administered to 982 first entering physics students; enrolled at three South African universities, at the beginning of the year before any formal instruction could take place. Data collected for this study included students' responses from multiple-choice questions and open-ended explanations to their chosen answers. The analysis of the multiple-choice responses and the written explanations revealed the existence of alternative conceptions among students and that the students' accuracy of judgment about their knowledge and understanding of basic mechanics concepts is different among the different cohorts. Physics education research, has over a number of years, revealed that students have alternative conceptions about physical processes. These alternative conceptions are accumulated from the students' past personal experiences, interactions with people around them and the environment they live in. It was found from the study that the strength of the known alternative conceptions differs among the different cohorts. There are those alternative conceptions that are easier to correct with sound teaching. These alternative conceptions exist mostly in worst performing cohorts and less so in the best performing cohorts. There are those alternative conceptions that persisted despite better teaching. These alternative conceptions are found in all the cohorts. The certainty of response analysis revealed the differences in the relationship between performance and confidence among the students from the three universities. It was also found that students make incorrect judgment about their knowledge and understanding of basic mechanics concepts. The overall trend emerging from the study was that students seem to be overconfident about their knowledge and understanding of basic mechanics concepts, but that students with a good command of mechanics concepts made the best judgment about the correctness of their answers. The item-by-item analysis of students' responses revealed that in most cases the best performing students make quality judgment about their performance, while poor perfOlming student always make inaccurate judgments about their performance. Analysis of the students' written explanations and item difficulty revealed that the Hasan et al. (1999) study is lacking in the differentiation between lack of analytical skills and the presence of alternative conceptions. Lack of analytical skills cannot be classified as evidence of the presence of alternative conceptions. The student may be having knowledge of the necessary concepts, but lack higher order analytical skills to be able to interpret situation presented.