This article presents the findings from a recent study funded by the Nuffield Foundation, which aimed to provide insights into the experiences of young people and teachers in secondary schools across Scotland under the Curriculum for Excellence (CfE). Our research has uncovered a decrease in the number of National Qualifications entries in S4 under CfE, a phenomenon commonly referred to in Scotland as ‘curriculum narrowing.’ Furthermore, we have identified evidence of social stratification in overall and subject entry patterns in S4, with students from disadvantaged areas experiencing a more significant decline in entries and being limited to a narrower range of subjects. Additionally, our study has revealed signs of curriculum fragmentation during the Broad General Education phase (years S1–S3). The findings from our study also suggest that the curriculum decisions made in schools are primarily driven by the demand for better attainment data, particularly in National Qualifications during the Senior Phase (school years S4–S6), with less emphasis on what it means for an individual to become an educated person in a modern and complex society. Based on our findings, we have concluded that curriculum fragmentation and narrowing under CfE have a detrimental impact on the progression and attainment of young people. Schools that offer a broader curriculum in S4 demonstrate higher enrolment rates for Higher qualifications in S5 and Advanced Higher qualifications in S6. In contrast, schools that offer a narrower curriculum in S4, particularly those in deprived areas, are more likely to experience delays in higher-level qualification entry. A broader curriculum in S4 has been associated with improved performance in National 5 qualifications, higher scores in international tests such as PISA English and Maths, and higher scores on OECD measures of global competences. On the other hand, a narrower curriculum is correlated with less favourable outcomes after leaving school, especially in terms of Higher Education enrolment.