College staff dialled 999 three times to report incidents of vandalism and threats from youths but police were too busy to attend.
When staff at Portslade Community College called the emergency number, they were left waiting hours for police to turn up.
On one occasion police were called to the college when youths gathered at the school gate during the day and threatened staff who asked them to leave.
The other two emergency calls were made when intruders and vandals were spotted on the campus in the evenings when adult education and sports groups use the college.
On two occasions, officers arrived hours after the alarm had been raised to ask staff if they still needed help.
The incidents were revealed by college principal Mike Tait following yesterday's report in The Argus about pensioner Thomas Didcott who tracked down his wife's stolen car but was told police were too busy to seize it.
Officers rang Mr Didcott the next morning to tell him they had recovered the missing Volkswagen Scirocco but left him with a £250 towing and storage bill.
Sussex Police eventually agreed to meet the cost of having the car towed away for forensic examination but Mr Didcott was told he would have to pay storage charges until it was collected.
Mr Tait has now told of his dismay at police not responding to emergency calls to the college in Chalky Road, Portslade, last year.
He said: "We have had three occasions when 999 was dialled and the police were not able to respond directly.
"If a school dials 999 you would expect a response. I was hugelydisappointed and upset by the response."
His complaints prompted a pledge from Brighton and Hove police to respond to emergency calls in future.
Policing in Portslade has recently been rejigged as part of a Neighbourhood Policing initiative, partly because of complaints about response times.
Mr Tait said: "I am not happy with the previous lack of response but I am optimistic from the assurances I have had."
There has been a series of incidents where police have failed to respond in the 12 months since Chief Constable ken Jones pledged to reverse the unspoken policy of not investigating minor crimes.
Another Brighton and Hove school drafted in security guards after police did not respond to a 999 call when an armed intruder was reported in the grounds.
Andy Schofield, headteacher of Varndean School, Balfour Road, said the incident could have resulted in serious injury or worse.
Sussex Police said new Neighbourhood Policing schemes were improving response times and senior officers had met with Brighton and Hove headteachers and would continue to work with them.
Chief Inspector Lance Gray, of Brighton and Hove police, said: "I am aware of two occasions where we were unable to send officers to Portslade Community College because resources were dealing with incidents elsewhere.
"However, we can also give examples where officers have been praised for their actions, most recently at a school in East Brighton within the last ten days."
Portslade councillor Bob Carden, who is a Portslade Community College governor, said: "There has been a number of similar incidents in the town where there has been a long response time, or no response.
"Since there have been changes things seem to be working. They are picking up incidents where they were not picking them up. It seems to be better than it was."
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