In this paper, we assume that students' achievement is influenced not only by a set of individual appraisals such as beliefs about their personal efficacy but also by a set of more systemic factors related to beliefs about their class efficacy as a group. Literature and research review supports that students' beliefs about their efficacy, both as individuals and as groups, are important predictors of their achievements at school. However, little research has been presented to date that jointly explores the impact of these two sets of beliefs on academic achievement. Therefore, the aim of this paper is to present an integrated view of individual and collective efficacy beliefs, exploring the relationship between them and their causal relationship with students' achievement. Two cross-sectional studies were developed in the Portuguese secondary school context with 385 and 1,794 students, using "Academic Self-Efficacy Scale" and "Students Collective Efficacy Scale" to assess individual and collective efficacy beliefs. The main results showed that individual efficacy beliefs were stronger predictors of students' grades than collective efficacy beliefs, especially when the specific domain of achievement they refer to was considered (for instance, levels of mathematics self-efficacy had a stronger impact on mathematics grades than on Portuguese grades). Moreover, moderating effects of gender and type of school (public vs. non-public) were found, suggesting that collective efficacy beliefs play a more significant role among boys and among students from public schools.