When members or representatives of a local congregation of a recognized church or religious denomination established for ten years or more within the state of Iowa prior to July 1, 1967, which professes principles or tenets that differ substantially from the objectives, goals, and philosophy of education embodied in standards set forth in section 256.11, and rules adopted in implementation thereof, file with the director of the department of education proof of the existence of such conflicting tenets or principles, together with a list of the names, ages, and post office addresses of all persons of compulsory school age desiring to be exempted from the compulsory education law and the educational standards law, whose parents or guardians are members of the congregation or religious denomination, the director, subject to the approval of the state board of education, may exempt the members of the congregation or religious denomination from compliance with any or all requirements of the compulsory education law and the educational standards law for two school years. When the exemption has once been granted, renewal of such exemptions for each succeeding school year may be conditioned by the director, with the approval of the board, upon proof of achievement in the basic skills of arithmetic, the communicative arts of reading, writing, grammar, and spelling, and an understanding of United States history, history of Iowa, and the principles of American government, by persons of compulsory school age exempted in the preceding year, which shall be determined on the basis of tests or other means of evaluation selected by the director with the approval of the state board. The testing or evaluation, if required, shall be accomplished prior to submission of the request for renewal of the exemption. Renewal requests shall be filed with the director on or before April 15 of the school year preceding the school year for which the applicants desire exemption.