The success of a deal struck to modernise Scotland's teaching sector is hard to judge due to a lack of "outcome measures", according to a report.
Teachers have more time to prepare lessons, the report said
Audit Scotland's review of the McCrone agreement found it had brought improved industrial relations, better teacher recruitment and retention.
However, it said headteachers' workload had increased since the 2001 agreement.
Education Minister Peter Peacock and Cosla said teachers were happier, but the SNP cited a "lack of focus".
A Teaching Profession for the 21st Century was an agreement between the Scottish Executive, Cosla and the teaching unions.
Audit Scotland's review identified increased opportunities for lesson preparation and professional development, with "protected time outwith the classroom".
The deal included a 23% pay rise for teachers over three years and the hiring of thousands more administrative and support staff to give them more time to teach.
However, the report said it was difficult to assess whether the extra funding was value for money because "clear outcome measures" were not included in the agreement.
Auditor General for Scotland Robert Black said: "The agreement is strong in detailing what needs to be done and by when, but it is less clear about how the cost and impact of the changes should be assessed."
Mr Peacock said the deal had enabled the sector to move away from a period peppered with strike threats.
"A Teaching Profession for the 21st Century is improving teaching in Scotland," he said.
"It allowed us to move on from a period of very poor industrial relations, peppered with strike threats, and to give greater respect and recognition to teachers in our society."
The minister said a four-year pay deal signed in 2004 gave teachers more stability and signalled an end to the dark days of the 1980s and 1990s.
Peter Peacock hailed morale within the teaching profession
"New teachers now benefit from the support and structure offered by the world leading teacher induction scheme," Mr Peacock added.
The minister said he would consider Audit Scotland's report in detail and consider how its recommendations could be used to improve the sector.
Cosla's education spokesperson Ewan Aitken said the teachers' agreement had brought lasting benefits to everyone within the education sector.
"Scotland's school children now have teachers who can concentrate on educating as a result of the recruitment of administrative and support staff to take on the non-teaching tasks," he said.
"Through the teachers' agreement we have delivered a modern, motivated teaching force that can only be to the benefit of our young people."
The EIS teaching union welcomed the findings, saying the agreement had brought "calm and stability" to industrial relations.
EIS general secretary Ronnie Smith said the report found the deal had a positive impact on Scottish education.
"Changing the climate and securing proper collegiate working in schools will take years to embed," he said.
SNP education spokeswoman Fiona Hyslop said the report showed the McCrone deal had been poorly implemented and failed to deliver all the expected reforms.