Concern over college severance deals
Several colleges did not handle cuts in the number of senior staff during a major reform programme as well as they could have, according to the public spending watchdog.
Audit Scotland said some of them did not follow good practice managing and approving severance arrangements.
The comments were made in a report on Scotland's colleges.
But it stressed that the changes have had a "minimal" adverse impact on students.
In the past few years, many colleges across Scotland have merged into regional "supercolleges" with the number of incorporated colleges dropping from 37 to 20 over three years.
According to figures included in the report, there were 238,000 college students last year.
This represents a fall of 19,500 on the figure for 2011-12.
Since 2009, the number of college students has fallen 36%.
The main reason for the drop is that colleges started to focus more on courses which led to qualifications and on young people - but more recently student numbers expressed as a full time equivalent have also fallen,
The report mentions "significant concerns" surrounding the way severance arrangements for senior staff at Coatbridge College were processed.
It also highlights a concern surrounding severance arrangements at North Glasgow College, which is now part of Glasgow Kelvin College, and says arrangements at four others - Banff and Buchan, City of Glasgow, Carnegie and Cardonald - fell short of good practice.
The report also warns it is still difficult to assess whether the reform programme across Scotland is achieving all its aims and that it is still not clear how much mergers have contributed to the savings so far.
It says the the Scottish government and the Scottish Funding Council have not specified the measures they will use to assess progress delivering the expected benefits of the mergers.
It added: "Neither could they provide us with details of the expected level of change required for mergers to be considered successful. The lack of baseline information for some of the expected benefits will also make it difficult to fully assess and report on improvement."
The Scottish government has indicated it will draw on existing data sources - such as financial data and college performance indicators - to assess progress.
Caroline Gardner, Auditor General for Scotland, said: "The last few years have placed significant demands on colleges in Scotland as they managed a complex programme of reform. Our report is intended to support them in learning from how these reforms were delivered and addressing areas that need to improve.
"In the main, colleges coped well with substantial changes to the way they work, maintaining sound finances and completing mergers on time, without negatively affecting students during the process.
"Many of the effects of the mergers are still taking place, however, and there are continuing challenges for the sector. It's important that the Scottish government and the Scottish Funding Council work with colleges to measure and publicly report on whether the reforms have delivered all of the intended benefits."
The organisation that represents colleges' collective interests, Colleges Scotland, said: "The report states that there were weaknesses in how a small number of colleges processed senior staff severance payments.
"It is important to stress that the decisions that were taken on severance issues were made by some pre-merger colleges, and not by existing colleges. The new guidelines and governance arrangements that are now in place provide a more robust system which should ensure that a similar situation does not arise in the future."
It added: "The Audit Scotland report recognises the significant change that the college sector has had to negotiate in the past few years. It underlines that colleges in Scotland have succeeded in delivering what has been asked of them on time, whilst maintaining sound finances, and protecting the learner.
"It is our understanding that no other sector has been re-classified from private to public sector - it has been unique for the college sector, and therefore there has been no precedent."