This article presents findings from a case study of an in-classroom program based on ability grouping for Year 2 (ages 6-7) primary (elementary) children identified as high ability in mathematics. The study examined the role of classroom setting, classroom environment, and teacher's approach in realizing and developing mathematical promise. The teacher's approach was found to be fundamental to revealing and developing mathematical promise. However, a large regular classroom with a range of ability, along with some common beliefs that link mathematical prowess with competence in numerical calculations and that dominate the classroom environment, pose some major challenges for the teacher as well as obstacles and threats to the development of mathematical promise. The article illuminates these issues and suggests possible solutions.