A public school district shall not discriminate against students or parents on the basis of a religious viewpoint or religious expression. A school district shall treat a student's voluntary expression of a religious viewpoint, if any, on an otherwise permissible subject in the same manner the district treats a student's voluntary expression of a secular or other viewpoint on an otherwise permissible subject and may not discriminate against the student based on a religious viewpoint expressed by the student on an otherwise permissible subject.