State and private agencies have attempted to determine the costs of providing an "adequate" education for public elementary and secondary students. In order to identify adequacy target expenditures, four education finance models currently are found within the education finance research literature: (1) Professional Judgment Model; (2) Statistical Analysis Models; (3) Evidenced-Based Model; and (4) Successful Schools Model. This article offers a specific research protocol for the Professional Judgment Model to strengthen its utilization while outlining the remaining three models. (Contains 1 table and 1 endnote.)