Naomi, The fat content of the milk varies so much that it might be quite a challenge for your seventh grader to explain. The best info might be from Paula Meier, but since I can't find my notes of her lecture, I'll tell you what I can find in Nutrition during Lactation. p 118 "Lipids are among the most variable and difficult nutrients to measure accurately in human milk: among women, the total fat content of 24-hour milk samples may vary from less than 20 g/liter to more than 50 g/liter." p. 122 "Using amino acid analysis, Lonnerdahl and co-workers foudn that the protein content of mature human milk was approximately 8 to 9 g/liter." p. 124 "In human milk, lactose is present in an aveage concentration of 70 g/liter." Knowing that fat has 9 calories per gram and that lactose and protein each have about 4 calories per gram, she should be able to calculate the caloric content. I make it roughly <15 to >23 calories per ounce. I think it's great that now the students are educating their teachers about breastfeeding!! You go Girl!!