Assessment items in science have traditionally focussed on science knowledge. However, since literacy has become more important in science teaching and as a result science assessments have introduced a larger range of item s that are able to assess science investigative skills and science understanding as well as science knowledge. This in no small part can be attributed to the influence assessments such as PISA and to a lesser extent programs such as the TIMSS. The shift towards investigative or science process items raises the question of how this change will affect student performance. This research explored a series of large scale international population tests (International Benchmark Tests; IBT), that used instruments containing a balance of both science process and knowledge items. The instruments were administered to nearly 22,000 students, both primary and secondary aged. Rasch DIF analysis and correlation analysis showed little difference between the performances on the two item types. The conclusion from this study suggests that regardless of the students’ ability they will perform equally well on science items regardless of whether the items have a process or knowledge focus. This result though somewhat surprising suggests that students are not disadvantaged by the changing focus of different questions