In my book, which is the 1996 Simon and Schuster hardcover version, Julian talks about the ivory monkey on page 97. Since page numbers vary from edition to edition of books, yours may not have the same pagination. It might be easier for you to find the account if I tell you that it is about four pages into Chapter 4, in that chapter's third section.
The ivory monkey was given to Julian by his wise old friend Gopal. The "little sculpture" can do "tricks"; it "can balance on any one of its four limbs". Julian uses the monkey to illustrate how The Souls can help Mrs. Olinski, who, having just come back to teaching after being rendered a paraplegic in an auto accident, needs assistance to metaphorically "stand on (her) own two feet". Some students in the class, recognizing her vulnerability, are taking advantage of their teacher's situation, trying "to get her off balance" through their insolent attitudes and bad behavior in class. The Souls decide to stick up for Mrs. Olinski, supporting her, and "giv(ing) her a lift" as she tries to get over this transition in her life.
After the The Souls, led by Mrs. Olinski, win the contest against Knightsbridge against tremendous odds, the sculpture is again mentioned, as Julian "rub(s) the little ivory monkey in his pocket". With their friendship and solidarity, the jubilant Souls have indeed helped Mrs. Olinski regain her confidence. This incident is described on page 138 in my book, or, more specifically, in the last paragraphs of Chapter 7).