How does Dickens use the Ghost of Christmas Past to reflect on Scrooge's childhood and his memories associated with that time in his life?

Charles Dickens writes that the Ghost of Christmas Past first takes Scrooge to his boyhood where he lives at a residential school.  He finds his young self alone at Christmastime in the schoolroom and is absorbed in books while his schoolmates are out and about.  We find out that Scrooge's childhood has been difficult.  His schoolmaster is very stern and his father is not a kind person.  The spirit describes young Scrooge as "a solitary child, neglected by his friends, [who] is left there still."  Scrooge is impacted by the spirit's description of his boyhood self and he sobs.  The spirit takes Scrooge to another time in the same place.  A young Ebenezer Scrooge is once again alone at Christmastime.  His younger sister, Fran, enters.  She begs him to come home with her, telling him that their father has changed and has become a kinder, gentler person.  Scrooge, speaking to the spirit, reflects sadly that his sister died young.  Scrooge's childhood is overall sad and lonely, which he reflects upon during his conversations with the Ghost of Christmas Past.