South Africa's National Senior Certificate examination system was introduced in 2008 as a single national examination system, in order to facilitate fair and standardised assessment and to provide all learners with an equal chance of access to higher education. However, limited research has been done to investigate the discrimination power of the actual examination items and the spread difficulty level for learners from different school quintile types. The purpose of the study reported on here was to investigate differential performance of learners in the items of the 2009 National Senior Certificate mathematics examination. The dataset used in this study was from the Western Cape (WC) Education Department. From the analysis, the results show that the discrimination power of the different examination questions was not identical across different school quintiles. Further investigation of the data reflects a considerable range of category difficulty levels, with higher (above average) ability levels being tested for learners in the quintile 1 to quintile 4 schools, while only learners with average abilities were being tested in the quintile 5 and independent schools.