Crews used 10 breathing apparatus, two hose reels, two jets, two compressed air foam jets and the aerial ladder platform to bring the fire at Winton School in Andover under control.
Group Manager Dan Tasker said: "The first crews to arrive were met with a challenging situation of a confirmed fire plus the evacuation of 500 pupils."
More top news
Wednesday night's weather for the east of the region
Wednesday night's weather for the west of the region
Simon's Blog - Things That Look Like Other Things