The Festival of Instrumental Music is four concerts over four nights in the Concert Hall at the Sydney Opera House, from August 3-6.

Nearly 3200 public primary students from 175 state schools in Years 3 to 6, including some from the Highlands, have been rehearsing all year to take part.

Each night has three set pieces - the Dance of the Tumblers, Rondo and The Swans of Lir - by 700 recorders and 200 strings.

The students must memorise the music as the recorders will perform sheet-free in the stalls while the strings are on stage.

Other school ensembles will play in between the set pieces, and some 2000 family and friends have bought tickets to look on.

Assistant principal of one featured school, Colo Vale's Anne Donaldson, called the recorder "a great instrument for children".

"It is the right size, it's affordable, it's light, and - played well - it's beautiful," she said.

But for Mrs Donaldson, it's the venue that takes the event from special to spectacular.

"You see all these other kids playing amazing instruments at amazing levels, and it just expands everyone's horizons," she said. "It's a new experience in a safe and guided setting, and we need those experiences to encourage life-long resilience in children."

Sydney Conservatorium of Music graduate Daniel Murphy will conduct Highlands students in one of the massed concerts.

His "cluster rehearsal" at Colo Vale last month had 150 students from 13 Highlands and Tablelands schools, and the sound was simply glorious.

"People's jaws drop: they can't believe recorders sound so good," Mr Murphy said.

"They want to do well so they practise. This is what we can do with public education, and it's really great."

Festival tickets have sold out, but see a little of Mr Murphy's rehearsal here: