I recently read a school started a new policy: kids who arrived late spent much of the day sitting in the auditorium as a punishment for the tardiness. My reaction to the article was one of sadness.
The past four Summers I have had the joy of being an administrator for our Summer School 9-12 program. When students arrive late, they are greeted with a warm smile, breakfast, a general check-in, and sometimes even walked to class. Why? I am glad they showed up. I want to know everything is alright. Sometimes (later in the day) there is the need to follow through with a more specific chat and perhaps involve parents. But for that crucial first moment, I am so happy the student arrived safely. I never want a child to fear arriving late. Otherwise, in their eyes, it would be better not to show up at all. That gets us nowhere.
Treat kids with respect. Listen. Problem Solve. Show you are willing to step up and help, no matter what.