The new Higher maths exam sat by pupils in Scotland this year was "more demanding than intended", the Scottish Qualifications Authority (SQA) has said.
Almost 143,000 students are receiving their exam results today after sitting the new Highers for the first year and National 4 and 5 qualifications for the second year.
The new qualifications were brought in as part of the Curriculum for Excellence reforms.
Pupils were also able to sit exams in existing Access, Intermediates and Highers which were "dual-run" for 2015 alongside the new qualifications.
Many students had complained that the new maths exam was more difficult than they had expected, with the SQA stating that its marking process had taken this into account.
A total of 10,854 pupils sat the existing Higher maths while 10,220 sat the new Higher maths.
The attainment rates were 73.1% and 70.8% respectively, similar to that of previous years.
Dr Janet Brown, SQA's chief executive and Scotland's chief examining officer, said: "As in every year, we carry out a review of assessments to ensure candidates have been able to display their skills, knowledge and understanding.
"If required, grade boundaries are adjusted to take account of any assessments that were easier or more demanding than intended to ensure all candidates received the grades they deserved."
SQA figures show that there were a record 156,000 Higher passes this year, up 5.5% on 2014.
Overall, a total of 107,295 pupils sat the new Highers, with a pass rate of 79.2%. A further 92,555 pupils sat the existing Highers, recording a pass rate of 76.7%, slightly down on the 2014 pass rate of 77.1%.
Higher English passes were up 17.7% to 27,902 and Higher modern languages passes increased by 15.2% to 7,419.
The pass rate for the National 4 was 93.3%, with 114,173 passes, while pupils achieved 229,870 passes at National 5 level, resulting in a success rate of 79.8%.
Advanced Higher passes increased by 4% to a record level of 18,899, with pass rate of 80.9%.
Education Secretary Angela Constance said: "This is another strong performance by Scotland's young people.
"They have worked hard and I congratulate each and every one of them, as well as the families and carers and teachers and lecturers who have provided support.
"Scotland has seen record numbers of Higher and Advanced Higher passes. Students are performing particularly well in English and in modern languages.
"Despite concerns about the new Higher Maths exam, it's clear that the system worked, that candidates have been treated fairly and that standards have been maintained."
Scottish Labour education spokesman Iain Gray said: "It is encouraging to see record numbers of exams passed and congratulations are due to all those young people whose hard work has paid off.
"We should also acknowledge that teachers have delivered under significant workload pressure and an exam system in flux.
"The concerns of teachers still need to be be addressed by SNP ministers, and they must do that soon."
Scottish Conservative young people spokeswoman Liz Smith said: "While it is important to congratulate all those pupils and teachers who have worked so hard to obtain their results, the Scottish Government must not lose sight of the fact that there is still a significant attainment gap between pupils from poorer and wealthier backgrounds."