For a three-act plot analysis, put on your screenwriter’s hat. Moviemakers know the formula well: at the end of Act One, the main character is drawn in completely to a conflict. During Act Two, she is farthest away from her goals. At the end of Act Three, the story is resolved.
Act I
The six narrators are children attending a nursery school together. In this early stage, they mostly play around outside, sit through their lessons, and think about what makes them special and distinct from the others. They are all special snowflakes.
They then go off to boarding school, where the boys meet Percival (who is introduced to the girls at some later point). After boarding school, Neville and Bernard go to university. Ultimately, they all move into adulthood and their respective careers.
Act II
Percival dies, sending the six narrators into crisis mode. They advance further into adulthood, reflecting upon the changes they are undergoing and boo-hooing about their distance from others.
Act III
The characters descend into old age and ponder their own mortality. At some point, Rhoda commits suicide. Bernard spends the final chapter attempting to summarize the book's events and their meanings and then resolves to fight against the forces of death and alienation that the characters have been struggling with throughout the novel.