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."
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Rain clearing east tonight for a dry but fresher day tomorrow with plenty of sunny spells.
Heavy rain clearing east for a dry but fresher day tomorrow with some hazy sunshine.
Rain becoming heavy at times this afternoon before clearing tonight. Dry with hazy sunshine tomorrow but feeling fresher.