Okla. Stat. tit. 70 § 9-108
The board of education of any school district furnishing transportation is hereby authorized to furnish, in addition to free transportation to and from school, transportation within or without the district, within or outside of this state, for children attending the schools of that district, for the purpose of attending cocurricular and extracurricular activities. Two or more districts may enter into agreements for the furnishing of such transportation. The expense of any such additional transportation shall be paid by the children so transported, by the school activity or school organization receiving benefit from such transportation, or from other private sources. Money so collected shall not be chargeable to or become a part of the school district's finances.
Okla. Stat. tit. 70, § 9-108