One boy is playing softly on the drums. Two others are working tentatively on a guitar duet. Elsewhere in the room, several boys are busy composing, headphones clamped to their ears as they sit at their keyboards jotting down ideas.
Until recently such a session would have been unthinkable. Now, as a result of radical changes in Dartford Boys' approach to the arts, it's a regular occurrence.
Elisabeth Cook, head of music for the past four years, remembers the old days: "We had no drama, and a very traditional music department which catered mainly for the musically able. There were also a lot of very talented musicians kicking around, but no orchestra. I wanted to change all that and get everyone to participate."
To broaden the subject's appeal, she made sure students engaged in practical music-making for most of their lessons, and were provided with plenty of opportunity to practise their skills. The school now has two choirs, an orchestra, a wind and jazz band, and many smaller music groups.
The students learn musical notation, and compose, listen to and perform a wide range of music: jazz, pop, baroque, blues, world. Many who have never performed publicly have gained confidencein doing so, and boys of differing musical abilities often work together. "The able musicians are not always the leaders, " says music teacher Mike Conn, the deputy head.
Last September the school took another bold step by introducing an expressive arts course for key stage 4, combining music and drama and giving students the option of including an element of art, design or dance. The boys can, however, still take music (and next year drama) as a separate GCSE.
"Mixing the arts in this way makes the students think a lot more about what they're doing, and why," says Ms Cook. "It also encourages them to experiment, and has a good knock-on effect for working as teams."
That team-work was evident in the school's recent musical celebration, Victory, put together for VE Day. The boys did the lot: music, stage management, sound, design, publicity, make-up, script writing, co-directing, as well as performing.
Today, during a post-mortem on the production, the Year l0 group talk enthusiastically about their collaboration and their chance to get involved in different art forms. Andrew Rye neatly observes: "It's hard to perform on the flute, but I can act, so when I'm playing it I make myself into an actor. "
The boys can take dance as one of their individual assignments, although Ms Cook accepts that there has been some resistance to it. Willlam Ladbrook-Hutt, aged 15 but already a seasoned dancer outside school, puts it more bluntly: "Everyone's scared to do it because it's supposed to be a gay profession. So you get the mick taken."
But progress is being made: involvement in world music, for instance, has brought in movement quite spontaneously and has encouraged a more positive attitude, explains Ms Cook.
These changes have substantially raised the arts profile in the school. Mr Conn pinpoints one significant outcome: "Often in grammar schools you get the sporting types and then the 'artists', as they're disparagingly called. Here you get boys who are genuinely talented at both."