Someday Angeline by Louis Sachar
Angeline is brilliant! She knows way more than a child of her age ought to. When she is moved up a class at school she finds that her intelligence doesn't equip her entirely for dealing with the pressures of being with the older group. Soon she is finding refuge with a teacher and her tropical fish and another unlikely student. With Louis Sachar's hallmark twist-and-turns of plot and lovely humour, this delightful novel is thought-provoking and brilliant.