The exemption set forth in 49 U.S.C. 13506(a)(1) shall not be construed as being inapplicable to motor vehicles being used at the time of operation in the transportation of schoolchildren and teachers to or from school, even though such motor vehicles are employed at other times in transportation beyond the scope of the exemption. [36 FR 9022, May 18, 1971, as amended at 62 FR 15421, Apr. 1, 1997]