You can't beat a graffiti wall for learning what people really think. Even the most reserved express opinions when given an expanse of blank paper and a cloak of anonymity.
While the discussion groups assembled last month in Oban's Corran Halls to shadow judge the Carnegie Medal took some prompting, many of the pupils from secondary schools all over Argyll and Bute had already "talked to the wall" and a clear favourite was emerging.
It was not the one criticised as "rubbish, a girls' story" - a comment which prompted the reply: "Girls won't like it either. It sucks."
Nor was it the book whose "best bit was the end", a barbed remark and not praise for clever plotting.
"A book to relish rather than rush" looked a better bet.
Schools can shadow this award, given each year to the writer of an outstanding book for children published in Britain, by setting up their own judges and putting comments on the Carnegie Medal website, explains Cheryl Wood, Rothesay Academy's librarian and a former English teacher.
"When we started six years ago, I thought it would be fantastic to get our kids mixing with those from other schools. So I took them to Dunoon Grammar. That was a great success, so the next year we went to Tobermory High on Mull."
Video conferencing equipment gave the opportunity to widen the reach of the Carnegie shadowing and in recent years most of the sprawling authority's secondaries have taken part. Last year they applied for an Awards for All grant to get children from all the schools together. "As you can see, we were successful," Ms Wood says, as she surveys the full hall.
School librarian Francis MacArthur, one of the real judges this year, explains the process of whittling 45 books down to the five the pupils are judging. "We looked at plot, characterisation and style, but a book also needs that X-factor that makes it stay in your mind long after you've finished it."
The Carnegie Medal was established in honour of the Dunfermline-born philanthropist who built more than 2,800 libraries around the world. Recent winners include Philip Pullman and Terry Pratchett, as well as three authors who made the shortlist again this year: David Almond, Geraldine McCaughrean and Jan Mark.
Among the discussions, the criticism most often heard is that a book does not make you think. Books with a dash of fantasy are proving popular. Ailsa Floyd, of Lochgilphead High, is unusual in finding simplicity appealing. "I liked Turbulence. It was an easy read but very enjoyable."
"Clay was my favourite," says Jamie McKinley, of Tarbert Academy. "It was confusing at first, but eventually you got right inside the minds of the characters." This is an essential quality to many.
"The main character in The White Darkness, which I really enjoyed, has given up on life and fallen back on an imaginary person she can relate to,"
says Gemma Shields of Dunoon Grammar. "A good book, I think, is one you have to work at."
A criticism of more than a few was voiced by Lachlan Lewis-Smith, of Rothesay Academy. "The winner has already been decided by adults. What is the point of a children's book award that has no children judging it?"
At the end of a day's discussion, Tamar by Mal Peet, the graffiti wall favourite, gets the vote.
"You can see the characters change and progress, and react to everything that happens to them," says Charlie Marshall of Hermitage Academy. "You can see the legacy of the things they do."
And who was the winner announced this month? Mal Peet.