OXFORD, Mich. — A group of Oxford High School students walked out of class Thursday, gathering on the football field after leaving the building. Footage posted on social media from other outlets shows the students standing in a “U” shape after filing from the school onto the field. It lasted for about half an hour. The walkout comes two days after a mass shooting at a Texas elementary school where 21, including 19 children, were killed. On Tuesday, the Oxford Community Schools officials held a moment of silence for the victims of the Texas shooting during a board of education meeting that was …