Huang Hu, a 30-year-old doctor, was detained on suspicion of lacing food at the school in south-eastern China with rat poison, Xinhua news agency reported.
Mr Huang opened his own school in Wuchuan in October but was reportedly jealous of his rival's success.
The incident follows a mass poisoning in September by a restaurant owner who was said to be envious of his business rivals in the eastern city of Nanjing.
The state People's Daily newspaper said on Thursday that 5,900 people were affected by food poisoning in China in the first 10 months of this year.
Popular poison
All survived the attack on Monday in Guangdong province but some of the 72 victims were still in hospital after suffering vomiting and fits, Xinhua said.
The poison used in the attack was reportedly the same kind as that used by Chen Zhengping, who was executed in October for poisoning breakfast snacks in Nanjing. At least 38 people died in that incident.
The same brand of rat poison was also found at the scene of two poisoning incidents in September in which five people died after eating at restaurants in the north-western city of Xian.
There have been several cases of poisoning in schools in recent years.
Last January, in Hunan province, 92 primary schoolchildren fell ill after their lunch was poisoned.
Bacteria and cases of restaurants using cheaper industrial salts instead of edible salt is to blame for some of China's poisoning deaths.
But the People's Daily said the number of poisoning victims this year was down 56% compared with the first 10 months of 2001.