Xin Ou primary school sent out a mass text message to Wenzhou parents on Tuesday that said "this student is basically a stupid piece of shit, how was s/he ever born?" Hong Kong-based South China Morning Post quoted local Chinese media as saying.
Angry parents asked school officials for an explanation.
A school spokesperson said the message was the result of a software malfunction.
The school had been using a software platform named "Education Baby" that allowed teachers to text parents about students' performances.
The system collapsed on Tuesday.
Someone could have hacked into the system to send the malicious message, the spokesperson said.
The school has issued a letter of apology to parents, who are still waiting for the results of the police investigation.
"I actually think this is what some teachers truly believe," said a netizen sarcastically on China's micro-blogging service Sina Weibo.
"The school needs to stop blaming others and face its own mistakes," said another Weibo user.
