A review of police call handing carried out after officers took three days to respond to a report of a fatal crash has highlighted how "insufficient staff" had resulted in "low levels of performance".
The report by HM Inspectorate of Constabulary in Scotland also pointed to problems with training and IT as it called for plans for further control-room closures to be put on hold.
The review, which was commissioned in the wake the deaths of John Yuill and Lamara Bell in a car crash on the M9 near Stirling in July, has made 30 recommendations for improvement - which Police Scotland has already said will be implemented.
HM Inspector of Constabulary Derek Penman said: "I have highlighted a number of weaknesses in Police Scotland's approach to the roll-out of its new national call-handling model.
"This model is a critical element in the delivery of frontline policing and a key part of the bringing-together of Police Scotland post reform.
"The oversight of this project has been inadequate with key risks and other issues not being identified or highlighted to senior managers."
The review recommendations should be addressed "as a priority", Mr Penman said, adding that Police Scotland should produce an action plan setting out clear timescales for delivering these changes.
While the report was commissioned following the death of Mr Yuill and Ms Bell, it did not consider why police took three days to follow up a reported sighting of their wrecked car.
Instead, it looks more widely at the operation, systems and processes in place within police contact, command and control (C3) centres across Scotland.
Police Scotland needs to improve workforce planning to "address previous weaknesses in assessing demand and ensuring that sufficient staff are in place at critical stages," Mr Penman said.
He added there were insufficient staff in place when work transferred to other locations following the closure of police control-rooms in Stirling and Glenrothes, and said: "This resulted in low levels of performance."
While the review found Police Scotland has made "considerable efforts to address this", it said there are still staffing challenges in the north of Scotland.
Although 999 calls are "answered quickly with a prompt response from officers", Mr Penman said: "The handling of lower priority calls can be affected by a lack of available officers to attend incidents and weak divisional management of these incidents, particularly in the east."
The review said while the IT system being used is "generally fit for purpose in terms of basic functionality", there was a common concern among staff about the suitability of some of the systems.
Training is now in place for all new staff, but this "varied greatly in duration, coverage and quality" in the eight regional forces that were in place before Police Scotland was set up.
"Further work is required to develop a comprehensive, nationally consistent approach," Mr Penman said.
He stated there was a "lack of clarity around the strategic vision for the national C3 model, with no alignment to wider policing strategy".
Brian Docherty, chairman of the Scottish Police Federation, said the organisation's concerns were "substantially borne out" by the report.
"We have consistently stated that the drive to save money was resulting in an erosion of service and creating intolerable pressures on those working within it," he said.
"We have also stated that there is little point answering calls quickly if there are no police officers available to respond to them.
"This report leaves no doubt that this was indeed the case and that our concerns were fully justified."
He said the report also backed up the organisation's concerns over targets.
Mr Docherty said: "We clearly welcome the fact that despite these problems the service has, through a much-needed injection of cash and the sheer professionalism of those working in the centres, been able to address the majority of the call-handling problems that were dogging the service in the recent past.
"We are, however, disappointed that despite our submissions, HMICS has failed to properly contextualise the reality behind the relationship between call centres, the eventual police response and ultimately how this impacts on community confidence."
He added: "The simple fact is this: Police budgets are being cut. With the best will in the world, these cuts will impact on service and no amount of reassurance on one narrow, albeit important, area of policing will hide that."