Okla. Stat. tit. 20, § 1206

The four elective members of said board of trustees shall hold office for two (2) years, except the members of the first board, who shall be divided into two classes, with two trustees in each class, one class holding office for one (1) year and the other class holding office for two (2) years. Immediately after the selection and election of said trustees they shall be divided into said classes by lot.