Fourth grade is about right.  Children in America are reaching puberty earlier.  Two events happen in third and fourth grades for some children.  Sometimes there is a sudden growth spurt which involves body odor or mild breast budding in girls or underarm hair.  Often these signs recede, stay the same for some time, or advances slowly into puberty. Girls are menstruating earlier these days in the fifth grade to seventh. Boys change voices at about 13.  Of course, this is affected by family history, ethnicity, and state of health. In fourth grade,most health classes may mention growth, what is normal or expected in time. You can take an active role to allay any concerns by discussing with your daughter what are your comfortable basics. That usually suffices fourth graders.
 
Wayne Yankus, MD, FAAP
expert Panelist: pediatrics