I’m a great fan of Ken Loach – the director of Kes but I can’t say I entirely approve of his approach to the welfare of his young actors. Loach is famous for wanting realism in his work and is uncompromising in how he gets it. Rather famously, back when he made a film called Cathy Come Home about homelessness in the mid 1960s, to get an accurate scene of a women’s children being taken away by social services, he didn’t inform any of the actors playing the family and had them suddenly attacked and the children dragged away screaming from the young actress playing their mother who genuinely believed they were being snatched.
And, yes, in Kes the boys were caned for real.
Bob Bowes who plays the Headmaster in that scene was a real teacher and appears to know what he was doing.