Colorado Revised Statutes Title 22. Education § 22-33-103. Free education--tuition may be charged, when

Any resident of this state who has attained the age of six years and is under the age of twenty-one years is entitled to attend public school in the school district of which he is a resident, during the academic year when the schools of the district are in regular session, and without the payment of tuition, subject only to the limitations of sections 22-33-105 and 22-33-106. Tuition may be charged for a pupil who is not a resident of the school district in which the pupil attends school if the school district of residence agrees to pay such tuition as provided in section 22-32-115. In no event shall the parents or guardian of such pupil be required to pay tuition on behalf of such pupil. Tuition may be charged to pupils whose parents or guardian are not residents of the state and to resident or nonresident adult pupils, as otherwise provided by law.