Gifted students continue to be under identified and overlooked in Australian schools despite policy recognition of their existence for over 50 years. However, even when identified, giftedness itself does not guarantee academic success, as these students require appropriate educational provisions to develop their potential. Australian research in gifted education has focused on interventions, attitudes towards giftedness, and teacher professional learning. Typically, studies focus on the areas relating to causes of underachievement or strategies and interventions for its reversal. There is limited research into teachers' qualitative perspectives on gifted student achievement and its influence on their expectations and provisions providing a justification for the conduct of this study. This qualitative study sought to explore Year 8 and Year 9 classroom teachers' perceptions of gifted student achievement, examining both the factors that teachers believe influence achievement and those that shape their perceptions, while accounting for the complex interplay of personal, social, and political factors. Teachers' perceptions of achievement within a bounded system were explored using case study methodology. Bronfenbrenner's ecological systems theory was used as the theoretical framework to support the exploration of how teachers perceived the achievement of gifted students in their classrooms. This theoretical framework supported the sociological perspective taken to explore how the complex interplay between classroom teachers, gifted students, and their broader context influences both teacher perceptions of gifted students' achievement and the development of gifted potential. This study aimed to reveal the factors teachers perceived as important in influencing the achievement of intellectually gifted students in Years 8 and 9, further exploring factors that shaped these perceptions from the perspectives of seven high school teachers through the following research questions: How do teachers define the achievement of gifted students?, How do teachers define and understand the expected achievement (potential) of gifted students?, What factors shape teacher perceptions of achievement for gifted students?, and What factors do teachers believe are important in influencing gifted students' achievement?. Five themes emerged from the data: (a) Summative assessment limitations, (b) Curriculum constraints stifling potential, (c) Gifted students as "other" or "separate", (d) Enjoyment and growth as achievement, and (e) Teacher uncertainty. Teachers viewed gifted students as distinctly different from their age-peers and felt conflicted between adhering to the perceived rigid curriculum and assessment demands and their desire to prioritise challenge, growth, and interest. While high summative assessment results were understood as the normalised and expected indicators of achievement, teachers recognised these scores as insufficient measures of gifted students' true abilities and potential, indicating the presence of a systemic learning ceiling. The perceived curriculum rigidity and assessment-driven teaching created a pervasive influence on classroom teaching practices, constraining teachers' ability to provide the challenging learning opportunities they perceived gifted students needed. There are four recommendations from the study: (a) the introduction of a Queensland state gifted education policy to create flexibility in curriculum implementation, assessment, and reporting for gifted students, (b) development of a supplementary curriculum for extension and enrichment alongside year-level achievement, (c) in-service professional learning for teachers and school leaders on the academic and social-emotional needs of gifted students, and (d) gifted education to be required in all initial teacher education programs. Future research directions include examining gifted students' voices to understand their lived experiences within these intersecting systems and investigating the development and implementation of effective initial teacher education and in-service professional learning programs to support the study's recommendations.