Children grow at different speeds, depending on the different stages of development they are going through. Sexual characteristics generally start to develop at 11.5 years of age for girls and 12.5 for boys. The first signs are the development of breasts in girls and enlargement of the testicles in boys.

Annual growth in height increases from 5cm before puberty to 7-9cm during the pubertal growth spurt. On average, this growth spurt is experienced by girls at the age of 12 and by boys at 14. However, differences in growth before the age of 12 should not prevent boys and girls from playing together.

Coach-educators should nevertheless take account of the difference between their chronological ages and their biological ages as well as any cases of precocious puberty when managing mixed groups to ensure they are well balanced.