Education secretary John Swinney has described a drop in the number of pupils leaving school with at least one exam pass as a "fluctuation".
He said Scotland had a "high-performing" education system, despite figures showing that the number of school leavers with at least one pass at National 4, National 5, Higher or Advanced Higher had all dropped.
The Scottish Conservatives claimed the Scottish government was "failing pupils of all ages and abilities".
The figures, published yesterday, showed the number of school leavers who had at least one pass at Higher level dropped from 62.2 per cent in 2017-18 to 60.5 per cent in 2018-19.
For Advanced Higher, the level decreased from 20.2 per cent to 19.1 per cent.
The Scottish government figures further revealed the proportion of leavers with at least one pass at National 4 level went from 96.2 per cent to 95.9 per cent over the period, with a drop from 85.9 per cent to 85.1 per cent for those who had at least one National 5 level qualification.
Mr Swinney acknowledged there had been “a slight fall in attainment” but added over time the percentage of school leavers achieving one or more passes at National 5 and Higher level had “improved substantially”.
The figures published by the Scottish government go back to 2009-10 and show that then just 77.1 per cent of leavers attained at least one National 5 level qualification and 50.4 per cent of leavers attained one or more Higher level qualifications.
Mr Swinney added: “We have commissioned the Organisation for Economic Cooperation and Development [OECD] to carry out an independent review of the curriculum. The review will look carefully at achievement in the senior phase so that we can improve further.”
However, Mr Swinney also said recently that he did not want the review of the Scottish curriculum to be “an extensive debate about qualifications”.
Figures show 28.7 per cent of school leavers had five Higher passes or more in 2018-19, compared to 30.4 per cent the previous year.
While 59.3 per cent of pupils from the least deprived areas went on to university, only 25.9 per cent of their counterparts from the poorest areas achieved this.
Overall, just over two-fifths (40.3 per cent) of those who finished school in 2018-19 went on to university, with more than a quarter (27.3 per cent) continuing into further education.
Over a fifth (22.9 per cent) went into employment, while 3.5 per cent found a training place.
Across Scotland, a record 95 per cent of school leavers went on to positive destinations – such as further or higher education, training or employment – within three months of leaving school.
The gap between the number of young people from the most and least deprived areas achieving this fell to its lowest level since 2009-10.
Meanwhile, the gap between the number of young people from the most deprived areas leaving school with at least one National 4 qualification, and those from the least deprived areas who achieved this, increased from 6.1 points to 6.7 points.
Mr Swinney said: "For the ninth consecutive year, more young Scots are in study, training or work three months after leaving school than ever before.
"Moreover, the gap between the richest and poorest communities for those moving into a positive destination continues to narrow."
He said this showed the Curriculum for Excellence education reforms were "delivering one of the ultimate aims of school education – to secure a positive next step in learning, life and work for our young people".
Conservative education spokesperson Jamie Greene said: "It's a complete disgrace that the attainment gap is growing again in certain areas, especially after all the noise the SNP has made about this issue over the years."
He added: "The SNP has been in complete control of education for 13 years. In that time, standards have slipped, teacher numbers have plummeted and now fewer youngsters are leaving with a qualification.
"Parents, teachers and pupils are absolutely fed up by this failing SNP government."
Labour education spokesperson Iain Gray said there needed to be a "whole-scale review of the badly implemented Curriculum for Excellence" and that jobs with zero-hour contracts were not a positive destination.
Liberal Democrat education spokesperson Beatrice Wishart said: "Pass rates fluctuate year-on-year but falls across the board expose the serious challenges facing Scottish education."