Parents are our children's first teachers and as such have the first and foremost right to control what is taught and shown to their children.   The government/school should only share with students what they have received explicit permission from parents to share and parents must be able to view in advance materials intended for use without obfuscation or denial due to charges levied or other methods of withholding the information.  There is no room for schools to expose students to sexually explicit content for any reason, most especially without parent consent and prior knowledge/approval.