[26] For example, these explanations include the retirement of an aging teaching force, increased student enrollments, reforms such as the reduction of class sizes, high rates of attrition, and lack of qualified candidates willing to enter the profession (Broughman and Rollefson 2000; Howard 2003; Hussar 1999).

[27] Teacher shortages occur in a labor market when demand is greater than supply. This can be the result of either increases in demand or decreases in supply or of both simultaneously (Guarino, Santibanez, and Daley 2006).

[28] Teaching vacancies in foreign languages, English as a second language, and special education were also difficult to fill in secondary schools, according to SASS data.