Plans to phase out Standard Grade exams as part of a radical education overhaul have been criticised by a teaching union.
Scottish pupils perform well compared to those in other countries
A team of international experts has questioned the usefulness of the exam in a major study into the performance of Scotland's school system.
But the Scottish Secondary Teachers' Association defended Standard Grades.
The report's findings were discussed at an international education conference in Edinburgh.
The SSTA said proposals to scrap Standard Grades "fail to take account of those subject areas such as modern languages where Standard Grade is an integral part of the process of learning a language and cannot be simply set aside".
But the union's general secretary David Eaglesham added: "The report shows clearly that the international team found huge amounts to praise in Scotland's system of education."
The expert recommendation came in a report which set out the strengths of the Scottish system but also detailed major challenges, including the achievement gap between youngsters from rich and poor areas.
The report by the Organisation for Economic Cooperation and Development (OECD) found that the biggest challenge of all was to make comprehensive secondary schools work consistently well and fairly.
The Educational Institute for Scotland, the country's biggest teaching union, welcomed the report, but said it was important that teachers were fully involved in deciding what changes should be made to the education system.
EIS General Secretary Ronnie Smith said: "If the changes set out are to have a real impact for schools and young people, the teaching profession as a whole must be fully involved in the discussions to come and the process of change.
"We welcome the OECD's recognition of the many positive characteristics of Scottish state education, such as the high performance of Scottish pupils compared to those in other countries, the highly equitable nature of our comprehensive education system, and our quality teacher development.
"Scotland is rightly proud of its education system, and it is important that we recognise and celebrate all that we do well in our schools."
The OECD report states that "few countries can be said with confidence to outperform it (Scotland) in mathematics, reading and science".
But it found that most of the difference in student achievement levels in Scotland was not due to differences between schools, but to differences within individual schools.
The report said: "In Scotland, who you are is far more important than what school you attend, and at present Scottish schools are not strong enough to ensure that 'who you are' does not count."
Suggested reforms include the creation of a Scottish Certificate of Education as a "graduation certificate" for all youngsters who complete a programme of studies or training - either in school, college or in a job.
The plan also includes making vocational courses available to all youngsters from S3 upwards.
And a more flexible relationship between schools and local authorities, and between councils and government, is also recommended.
In particular, it said councils should negotiate agreements giving schools more freedom over staffing and the curriculum - in return for progress on agreed improvements in "learning opportunities and outcomes".
Examiners from Australia, New Zealand, Finland and Belgium visited Scotland in March, and also studied research data.
Education Secretary Fiona Hyslop said: "The review shows there are some significant strengths in Scotland's schools but also some real challenges for the future."
"It also gives a series of recommendations which this government is well placed to meet."