When eight students with a mix of autism, cerebral palsy and Carpenter's syndrome step onto the stage at the Royal Albert Hall, London, this month, it will be the culmination of three years of musical achievement.
It became clear how talented they were, she says, as they progressed annually through regional and national heats of the National Festival of Music for Youth in Birmingham. The school backed them by investing in high-quality tuned percussion instruments: soprano, alto and bass metallophones and wooden glockenspiels.
Judith picked music that suited their strengths: "They have an amazing ability to memorise long sequences of notes. We're playing 'Time Lapse' by Michael Nyman, which starts off with a very basic bass part and builds up in layers. And a piece by Chris Hiscock.
"It's important not to underestimate these children. The idea of autistic children living in a world of their own is a fallacy. Music has the capacity to break down barriers. They work in groups, they are talented and motivated to get it right. And there's no conductor.
"One of the judges at Birmingham commented that their ability to listen and communicate non-verbally through their playing was astonishing.
"When one of our students came off-stage he said, 'We were really good'.
For him that's amazing as he's virtually non-verbal. We were good compared with all these amazing Yehudi Menuhin school string players. To be able to stand in front of an audience and know that you're fabulous: these will be memories they'll have for the rest of their lives."