We had terrible problems with parents parking dangerously. Notes home had no effect. Sometimes senior staff would go out to reason with the offenders, limited effect. Once, a child was knocked over (not badly hurt) by a distracted parent driving off carelessly - more letters home, assemblies to try to get the pupils to influence their parents. It worked for a limited time - but even then, not with all parents.
Baldric, before teaching time starts all the staff not on duty in the playground to control arriving children are in a morning staff meeting, getting notices about last minute changes, events happening that day, little Johnny or Ali needing an eye kept on him because grandma has died and being given details of which lessons they have to cover in their non-contact period because a colleague has rung in sick. After the close of lesson bell they are usually involved with disciplinary issues, departmental meetings etc., etc.. I know staff are not having their classroom time affected before and after school, but it is time still being spent in the process of education. :)