Grip mats which had been laid on decking outside three classrooms had been torn up.
Mrs Taylor said the brass sundial top had been fixed to a sturdy block and concrete base: "It was so heavy it took four guys to lift it back up again."
She said a visitor staying at a nearby house was awakened in the early hours of October 7 by the sound of men's voices. They also heard what they said sounded like a large car engine, similar to a V8, and a "massive crash".
She suspects the thieves had tied a rope from their car to the brass gnomon pointer and tried to pull it off. It wrenched the sundial free but also pulled the whole base over.
On the same night, the Marine Parade sundial was also targeted. Police said the incidents had to be linked, and that it is believed the thieves were after the brass.
Metal recycling firms across the region had been alerted but no information had come forward yet. Police want to hear from anyone who may have seen cars or people in the areas of the school and Marine Parade gardens on October 6 and 7.