In chapter four, the narrative delves into the Senior school experiences of the girls, marking a significant shift in their academic and social milieu. The initial allure of Senior life, characterized by amiable teachers and captivating new subjects like geometry and Greek, gradually wanes. Initially enthralled by the novelty, the girls find themselves confronted with the reality of Senior school, and the initial excitement fades as the "party-game effect of that first week" diminishes.

A retrospective scene unfolds years later, with Rose expressing remorse during a visit to Sandy at the Convent. She regrets not being kinder to Mary, hinting at a betrayal that adds an undercurrent of tension to the narrative. The story revisits a pivotal moment at the Braid Hills Hotel, where Miss Brodie contemplates the possibility of Mary's betrayal, expressing a regretful acknowledgment that she too should have been kinder to her.

The chapter also explores the Brodie Set's evolving dynamics, which face cohesion challenges. Miss Brodie's diminishing presence and Miss Mackay's attempts to disrupt the group contribute to the potential unraveling of their identity. Miss Mackay introduces schemes to break the girls apart, including assigning them to different houses at the Senior school to foster competition. However, the girls, instilled with a sense of individualism by Miss Brodie, resist the intended effect of these schemes.

Miss Brodie continues to exert influence during this period, hosting tea sessions for her girls on most Saturdays. She imparts a sense of exclusivity to her girls by downplaying the potential of her new pupils. Meanwhile, discussions about their art teacher, Mr. Lloyd, reveal an incident where he reacted negatively to the relaxed behavior of the girls. Miss Brodie's interest is piqued, especially when informed about Mr. Lloyd's admiration for Rose Stanley's profile, adding a layer of intrigue to the unfolding narrative.

At this point, the girls assume Miss Brodie is sleeping with Mr. Lowther to get over her love for Mr. Lloyd, who is married and unattainable. Miss Brodie begins grooming Rose to have a sexual affair with Mr. Lloyd when she is older. Soon after, Mr. Lloyd paints a portrait of Rose and then all of each of the girls.