The findings come from a report published by Fair Funding for Our Kids.
In 2014, the Scottish government increased entitlement to free childcare for three to five-year-olds from 475 to 600 hours per year.
A Scottish government spokeswoman said 2015 statistics showed "97% registration" for funded childcare.
Fair Funding for our Kids submitted Freedom of Information requests in order to analyse whether working parents' needs were being met across Scotland.
The research found that some local authorities were only offering half-day places at council nurseries.
While some families could place their children in private nurseries for the full day, councils did not always fund these places, even where the nurseries were in partnership with the local authorities.
The FOI requests found that in 2015/16 almost three-quarters of all free childcare places for three to five-year-olds in Scotland were offered in council-run nurseries.
The results showed councils in Scotland were underfunding places in private nurseries, with 25 of 32 local authorities offering an hourly rate below the national average cost of a nursery place.
A spokeswoman for the campaign said the results showed there had been "very little progress" made in ensuring Scottish parents could access the childcare they were entitled to.
Scottish Labour education spokesman Daniel Johnson said: "We need to see childcare policies that fit around the lives of working families, not just on an election leaflet."
However, a Scottish government spokeswoman said there had been "97% registration for funded entitlement to early learning and childcare for three and four-year-olds".
She added that the Children and Young People Act "put flexibility on a statutory footing for the first time" resulting in local authorities being required to consult with parents on childcare that would "best meet their needs."
Alison Johnstone MSP, the Scottish Greens' children and young people spokesperson, said that childcare arrangements in Scotland were "woefully patchy and inflexible," and added that as well as increasing the hours of free childcare, there was also a need to raise "the quality training and pay for childcare staff."
Johnstone added: "If we invest in good quality childcare there's a better chance of tackling unemployment, giving parents easier access to further and higher education, and reducing inequality."
FOI requests were submitted to all 32 of Scotland's local authorities. When analysis began two local authorities (Highland and North Lanarkshire) had not replied.
A report carried out by a campaign group has revealed some parents are struggling to access the childcare they are entitled to.