Five emergency crews were called to The Lakes College in North Lakes before 10am to reports of students suffering in the heat.
Queensland Ambulance acting operations supervisor Jen Pearce told reporters the students were part of an outdoor parade celebrating a new building when they began suffering from dizziness, nausea and headaches.
A teenage girl was taken to Prince Charles Hospital, a teenage boy to Redcliffe Hospital and another teenage girl to Caboolture Private Hospital.
All patients were in a stable condition and 13 other students were treated at the scene by paramedics.
A Lakes College spokeswoman told Fairfax Media late on Friday the only person able to comment had left for the day and the school didn’t want to answer any further questions.
Health officials have issued warnings for the intense heatwave much of Queensland is set to face at the weekend, with records expected to be broken.
Brisbane was expecting a top of 39 degrees on Sunday, but Birdsville could reach 46C, with temperatures about nine degrees above the February average.
Southerly winds would bring a brief reprieve on Monday, with maximums of 36C forecast.
Gold Coast beaches were also closed on Friday and a very high fire danger was also in place for the weekend in the south-east.