Various reasons can cause delayed puberty in boys and girls. The endocrinologist will systematically look for chronic diseases which can interfere with growth. Common diseases like thyroid diseases and certain drugs like steroids needs to be evaluated. Then they will look for various diseases which may cause reduced production of testosterone (in boys) and estrogen (in girls).
One of the most important things done by the endocrinologist is a careful clinical examination of the child. As the hormones in this age can be very variable, only a clinical examination and follow up can help understand the progression of puberty.