Janice - check out this document that helps to explain a bit more about some of the differences between a Public Account, Organizational Account, and Developer Account.
https://esri.app.box.com/v/agousestrategies
https://esri.app.box.com/v/agousestrategies
Another way to think of a Developer account is that it is a "one-person organization account." It is free to acquire and you have access to similar functionality that is possible in an full-fledged organization account. K12 has access to organization accounts through the ConnectEd program, but other non-profits or businesses must pay for Organizational accounts and for credits. So if someone doesn't have access to an Organization, they could create a Developer account to do analyses, create web mapping applications, etc.