Kids showing up late interrupts the entire class. The teacher has to repeat everything for one special little snowflake and the rest of the class gets annoyed. Back in the day, we got spankings, had to sit in the office and miss all of class or had our desk moved into the hall. Sitting by himself is a very mild punishment. Maybe, tomorrow, little snowflake will encourage Mama Snowflake to get her butt into gear and get him to school on time.
Again, what did this first grader do to deserve public humiliation?