A scientific model is a representation model for a certain scientific concept. Scientific models make it easier to study a phenomenon as they tend to model out the exact phenomenons.
A drawing of an skeleton would be unclear as the children might not be able to locate certain features in the drawing. For example, a certain joint could be missed by the teacher in the drawing or the child might not exactly be able to locate where the joint or bone is present.
But as the model will be more real to the actual skeleton system hence, studying through a skeleton will make it a lot easier to study the human skeletal system.