Nine-year-old boys are generally 126.5-137.8cm tall, and if they are below 126.5cm, they are short. In a sense, height is a nutrient build-up, so nutrition is especially important at this time. Height is also related to sleep, generally sleeping well and growing taller. The growth of height depends on the continuous growth of the epiphysis, which in turn is controlled by the endocrine glands. The endocrine hormones that control the growth are mainly growth hormone, luteinizing hormone and sex hormone secreted by the pituitary gland, among which growth hormone has the most significant effect, and the secretion of growth hormone has obvious regularity, with less secretion during the day and more secretion during sleep at night. Genetics is also related to height, and 75% of the final height of the human body depends on genetic factors.