Assessment of student learning for qualifications has long been contentious, particularly the reliability and validity of various assessment methods and the impact of assessment on the nature of student learning. There is, for example, controversy about norm-referencing versus standards-based assessment of student learning with different stakeholders holding different political agenda. In this study these issues are investigated by research into a recently implemented qualification for secondary school students in New Zealand - the National Certificate of Educational Achievement (NCEA). Proponents of NCEA suggest this regime acknowledges a wider range of student achievements than previous qualifications. Opponents of NCEA lament the 'fragmented', 'atomistic' approach to learning, and the lack of incentive for students to compete and strive for excellence. While other New Zealand research reports on national trends in the way school programmes are responding to the changes associated with the implementation of NCEA, little is known about the classroom curriculum students are actually achieving. This interpretive study presents findings from classroom-based case studies investigating the nature of the student-experienced curriculum for the NCEA Science Achievement Standard 1.1 Carrying out a practical investigation with direction. These findings indicate that the achievement standard is exerting a strong influence over the nature of student learning, with students experiencing purposeful and focused learning within a structured teaching programme. The emphasis in the standard on fair testing has implications for students' understanding of the nature of scientific inquiry by limiting their exposure to the range of methods that scientists use in practice. Student learning tends to be mechanistic and superficial rather than creative, critical and life-long. The findings have important implications for writers of national curriculum and assessment policy and for teachers of science. Suggestions are offered for ways of enhancing the learning of science under the NCEA qualification.