This paper reviews methods which have been used to identify and validate learning hierarchies. Specifically, three methods which reflect the notion of a relatively inviolate sequence are discussed and compared. Two of the psychometric methods compare pairs of skills, the ordering-theoretic method (Bart and Krus) and the test of inclusion (White and Clark). Dayton and Macready's method considers the hierarchy as a whole. Logical and empirical analysis with respect to the application of each of these methods to a common set of data (regarding a tenth grade chemistry concept) are reported. Results suggest that each method has some advantages. A modification of the White and Clark test, which enhances its generalizability, is also described. (Author/RD)