A study done in 2003 showed that teenage girls achieved optimal calcium accumulation with a daily calcium intake of 1,200mg per day.  The average teenage girl consumes a mere 500mg of calcium from her diet, therefore providing an additional 700mg per day with a calcium supplement is crutial. 

In an ideal world, teenage girls would consume 1,200-1,500 mg of calcium a day from food, go to the gym, and lift weights thre times per week, perform aerobic exercise regularly, avoid foods that rob the body of calcium such as: soda, salty foods, alcohol, caffeine, and cigaretes; and get the full spectrum of other bone supporting nutrients including vitamin D, magnesium, zinc, copper, B vitamins, silicon, an protein.