A report, compiled by Upper Quartile on behalf of Scottish Enterprise, suggests hundreds of firms being put forward are unable to increase their turnover quickly enough to meet the criteria to become an account-managed business at Scottish Enterprise.
Around 300 have been stuck on the pipeline, designed to help the transition between Business Gateway support and Scottish Enterprise account management, for more than 18 months, while some people consulted also questioned the quality of companies entering the process.
The target for Business Gateway companies is to see turnover increase by at least £400,000 over three years with businesses entering account management through other referral methods having to show an ability to increase turnover by more than £800,000.
The research - Evaluation of Scottish Enterprise Engagement with Account Managed Companies - concluded the pipeline is not "working as effectively as it could". However, it said it was unclear whether the wrong companies are being entered or if the support being offered is inadequate.
The report recommended a review of the pipeline to make sure both Business Gateway and Scottish Enterprise have an understanding of the entry and exit criteria. It also called for an examination of whether businesses in the pipeline have the correct levels of support, particularly as once a company gets into account management there is no difference in quality whether it has come through Business Gateway or another referral method.
Rhona Allison, director of company growth at Scottish Enterprise, said the agency has a commitment to continuously improve its programmes. She confirmed there are monthly meetings with Business Gateway where the growth pipeline is being "actively" managed.
Hugh Lightbody, chief officer at Business Gateway, said: "We have been going through a difficult set of economic conditions and some businesses have been concentrating on surviving and paying off debt. I think we will begin to see more companies coming through to meet their growth potential in the coming years."
The report also found every £1 spent on an account managed company generated £5.30 for the Scottish economy.
A separate study showed Scottish Enterprise's account-managed companies increased their turnover by 8% from £12.7 billion to £13.7bn between April 2012 and March this year.
Those in the oil and gas, food and drink and technology sectors made the greatest contributions.