Teacher brands students hand with a cross

The difference between state policy and religion is a matter of deep controversy in the United States, and also a policy that is enshrined in the US constitution, reinforced by many court rulings in the past. Hence, for a teacher to try and enforce his Christian beliefs (however fundamental these beliefs would be) on impressionable students is something that a number of people would disagree with. The teacher used to keep a copy of the Bible in class, carried the Ten Commandments, and also preached that evolution was flawed (against the education board policy):

The school board of a small central Ohio community voted Friday to fire a teacher accused of preaching his Christian beliefs despite staff complaints and burning the image of a cross on students' arms, according to the Associated Press.
Freshwater also displayed the Ten Commandments in his classroom and taught creationism, according to an independent investigation launched after the parents of the student who was allegedly branded filed a lawsuit. The suit alleges that he regularly discussed Christianity in his science class, even "teaching the meaning of Easter and Good Friday," and kept at least one and sometimes several Bibles in the room.

If teachers started teaching as per their own personal beliefs, then the entire education system would get flawed.