Sorry... what is no surprise? That the term 'species' is rubbery and not clearly defined?*
Its been clearly defined by myself in other threads, as well as by Stripe and others. Musterion defined it in this thread..."A basic type or model of organism created as distinct from other models, within which is the capacity for considerable variation (wolves, coyotes, mastiffs, chihuahuas, etc)."
You said you were interested in the definition of 'kinds' for education purposes. Its easy to find articles on the topics such as...
http://creation.mobi/variation-information-and-the-created-kind
Or, if you want something more technical, there are articles in peer reviewed journals such as this one from 'Answers Journal'..."An Initial Estimate Toward Identifying and Numbering Amphibian Kinds within the Orders Caudata and Gymnophiona
Jan. 23, 2013, pp. 17–34"