Attainment fell slightly across most of the Scottish qualifications published on Tuesday, leading to claims the SNP’s education drive is not working.
But UCAS admissions figures showed a record a number of young people from the most deprived areas getting into university.
Opposition parties accused Nicola Sturgeon of failing to deliver on her vow to make education the defining mission of her premiership.
The Scottish Qualifications Authority (SQA) published exam results for 135,000 pupils on Tuesday.
The A-C attainment rate for Highers has fallen slightly to 76.8%, from 77% last year and 77.2% in 2016.
For Advanced Highers the pass rate is 80.5%, up on last year’s 80%, according to the SQA data.
The latest National 5 results revealed a success rate of 77.4%, which is down on 79.5% in 2017.
Attainment was at 91.1% for National 4 exams, compared with 92.8% last year.
The number of entries in both National qualifications was significantly lower following a drop in the pupil roll and some restrictions to subject choice at S4.
Education Secretary John Swinney said: “Results day is a time to celebrate the achievements and dedication of learners right across the country, especially in this the Year of Young People.
“Higher passes remain stable despite a continuing fall in the number of young people on the school roll while the number of Advanced Highers being taken continues to grow.
“It is important to remember that we will always see slight variations in pass rates and the results show that we have a robust, credible assessment system in place.”
Opposition parties congratulated pupils, but raised fears about falling attainment levels.
Liz Smith, for the Scottish Conservatives, said: “There has been no improvement in overall attainment across the board and these statistics confirm there are still major issues about the mix between National 4 and National 5 qualifications.
“That’s down to decisions this SNP government has taken, and exposes the complacency it has shown towards education.”
The SNP’s pro-independence partners in Holyrood, the Scottish Greens, said the third annual drop in row for Highers results is concerning.
Ross Green, the Green MSP, said: “The SNP promised education would be the defining mission of this government but so far there isn’t much evidence of their mission succeeding.”
Iain Gray, for Scottish Labour, suggested that years of cuts to school budgets and teacher number are taking their toll on exam results.
“The SNP promised education would be the defining mission of this government but so far there isn’t much evidence of their mission succeeding,” the Lothians MSP said.
Meanwhile, figures from the Universities and Colleges Admissions Service (UCAS) show 29,830 Scottish students have had their UK higher education places confirmed, up 4% on last year.
The total number of acceptances from the one-fifth most deprived areas in Scotland increased by 5% to 4,340, the third year in a row a that a record figure has been posted.
Mr Swinney said the figures demonstrated “good progress” on widening access.
NUS Scotland president Liam McCabe said that is encouraging, but added: “We can’t lose sight of the fact there is much more to do to ensure more students from the poorest areas make it into higher education.”
Dr Janet Brown, SQA’s chief executive and Scotland’s chief examining officer, said the results are “testament to the hard work and dedication of the thousands of candidates across Scotland”.
Skills Development Scotland (SDS) has a dedicated exam results helpline on 0808 100 8000.