NeverTwerkNaked
Well penny I think the point is more that a primary school teacher is highly unlikely to be skilled at identifying natural talent in every single field.
Sometimes talent doesn’t show until it is given a chance.
You can bet the children who attend drama group after school or weekends will be more confident, better speakers, better dancers than those who don’t.
Same for sports - those who attend football/rugby training on weekends will have an idea of how to kick a ball and has learnt about contact and spatial aweness.
What about the well mannered, well behaved children? They have a better chance of becoming prefects as they are good role models. Or should the clown of the class who is regularly sent out of class because he is disruptive get to be a prefect because, you know, all children should be given the same opportunities.
Or the child who is way behind his peer group in lessons- should s/he be put forward to represent the school in academic awards?
Obviously teachers are going to choose pupils who are best suited for their drama roles, school sports teams, prefects, academic awards etc
I always find it funny that children who have no interest in performing arts suddenly have to be given the star role in their school production - because that bratty child who attends costly, intense Drama/Singing/Dance classes as well as singing and dance competition (and wins) gets a big part every year 
If a child has no talent in the drama stakes teachers usually choose the kids who have big personalities and are naturally funny. They are much more entertaining than shy, quiet children who, at best, will mumble their lines. At worst will be overwhelmed with an audience and become upset.
I am sure auditions will have been held even if not on the scale of X factor auditions. Plus teachers know the children in their class, therefore, will have a good knowledge of those who are most suitable and those who run the risk of crumbling and having their confidence rocked.
All children get a role in school productions whether it be Mary (not the best role tbh but usually given to a quiet child as Mary doesn’t usually have a speaking part) or whether they are part of the choir.
Parents should be telling their children that every role is important as without a chorus there would be no production. Give the kids a chance and stop coveting the main roles year after year. By the end of primary most children will have had at least one line to say whether it be at nativity or assembly. And many will be representing their school at sports events.