I've worked with many parents who are worried about their child's weight.  And why wouldn't they be – not only does our culture obsess about it, but often times their pediatrician does too.  What's frustrating to me is the lack of understanding by physicians of adolescent growth charts. 

Most docs carefully track growth during infancy as a way to ensure that the baby is developing properly, but by the time the child has reached adolescence the growth charts are often either abandoned or ignored.  And this can be a huge problem. 

For example, if a child's weight has always been at the 95th percentile on the growth chart, it's unreasonable to call that child overweight and flat out dangerous to recommend weight loss.  But parents don't know this.  All they hear is their child's doctor saying that he/she is overweight.  And then the well-intended parents tend to do some of the most detrimental things possible by putting the child on a diet, restricting their food, making shaming comments about weight or forcing the child to exercise.  This poor child has now been set up for a lifetime struggle with food, weight and body image. 

The normal amount of weight for an adolescent to gain is higher than most people realize.  Remember, they are still growing all the way into their 20's, and the increase in weight includes increased height, muscle, body fat, and bone density.  Attempts at losing weight or preventing weight gain during this time can be devastating and interfere with healthy development. 

Female

• 7-13 years old: pubertal changes begin in girls
• noticeable perspiration, body odor, acne
• 10-16 years old: growth spurt
• 40 lbs weight gain
• 6-9 months of increases in body fat before growth in height
• 13 years old: average age of onset of menses
• 11-15 years old: average range of first menses
• 16-20 years old
• 10-20 lbs weight gain
• weight gain continues until height growth stops

Male

• 9-14 years old: pubertal changes begin in boys
• noticeable perspiration, body odor, acne
• 12 years old is the average age for onset of puberty
• 12-16 years old: growth spurt
• 45 lbs gained
• simultaneous increase in muscle development and height
• 16 years to early 20’s
• weight gain continues until height growth stops
• 20 lbs gained

Source:
Herrin, M. (2007). The Parent’s Guide to Eating Disorders. Carlsbad, CA: Gurze Books.