Framey - you are making a good point and that what is needed is for the school to communicate effectively with the parents.
If it were made clear from the word 'Go' that the teaching time ends, for example, at 3.30pm, following which the children will have to get organised with coats, lunchboxes, bookbags, letters home etc, then parents will know that their children will be coming out closer to 3.40pm, and can make their after school arrangements accordingly.
But the way to achieve this communication is not by rudeness and arrogance as demonstrated by the OP, but by contacting the school and discussing the issue politely. Ask what time the teaching time finishes, and ask that it be made clear to the parents that this is the time the teaching finishes, not the time they can expect their children to arrive in the playground.
And if you have a specific issue, then discuss it with the teacher - princesspetty could have explained her timing problems to her dds' teachers, and asked if they could come out first, at 3.30pm on tuesdays - she's far more likely to get understanding and cooperation that way.
If I were the head of a school where a parent was regularly barging into their dcs' classes to get them out before the rest, to suit themselves, I would be banning said parent from the playground, and insisting that they waited in reception for their children to be brought to them. Now that would delay her!!