We are going round in circles now. As has been said, people have expressed strong views on this issue and those people will not be changing their views now.
It is a parents responsibility to ensure that their child gets to school on time. The trouble is that at secondary school age the children often make their own way to school as opposed to being dropped off at the gate by their parents. Parents would assume that the children get there on time unless notified otherwise.
Once the parents have made sure the kids have left the house on time they would not expect their child to take a detour to school via the butty shop. A responsible parent would be mortified if they knew that this was going on.
A responsible parent would applaud a teacher who spotted their child in the butty shop and ordered them to school.
To be quite honest though, the odds are quite high that a child sitting in a butty shop when they should be in school is not the offspring of a responsible parent. Not necessarily of course but quite probable.
There are several contenders for mum of the year on here.....myself, Bernadette, Katex, Gayle, Westender to name but a few.
No-one who gave a damn for their kids education would fail to back that teacher for what she did.