Just such a case was taken to the Press Complaints Commission by an aggrieved parent, who claimed that the juxtaposition of a photograph and a story about disruptive pupils implied that the pupils shown were disruptive. The Press Complaints Commission upheld the complaint and the paper had to apologise.
The guidance given to editors on this point indicates that photographs should not be taken on school premises without the school's explicit consent. Off the premises - outside the school gate, for instance - is another matter. In this case, if the picture is just a general one, incidental to the story, there should be no problem, but if either the story or the caption could be said to reflect adversely on the pupils shown, then it ought not to be used.
Where the story is directly about a pupil or pupils, no photograph should be used without the permission of the parent, or of an adult responsible for the child.
Unfortunately, there have been cases where parents have given their permission, with consequences for the pupil which can only be guessed at.
It might be possible in some circumstances to invoke the law of libel, although the law requires a minor to sue through a "next friend" adult. This is likely to be expensive, lengthy and may fail.