For the purpose of this chapter "adult education" shall be defined as set forth in RCW 28B.50.030 which provides as follows: "Adult education" shall mean all education or instruction, including academic, vocational education or training, basic skills and literacy training, and "occupational education" (chapter 180-51 WAC) provided by public educational institutions and community-based organizations, including common school districts for persons who are eighteen years of age and over or who hold a high school diploma or certificate: However, "adult education" shall not include academic education or instruction for persons under twenty-one years of age who do not hold a high school degree or diploma and who are attending a public high school for the sole purpose of obtaining a high school diploma or certificate: Nor shall "adult education" include education or instruction provided by any four year public institution of higher education.