The number of students dropping out of further education has more than doubled in four years, according to Scottish Labour leader Kezia Dugdale.
She said the number had risen from 934 in 2011/12 to 2,256 in 2015/16.
The figures are taken from six-month periods, with the latter representing the equivalent of 12 people each day, according to the party.
Ms Dugdale raised the issue at First Minister's Questions at Holyrood as a new report indicates the number of full-time equivalent students in Scotland's colleges fell last year.
She said: "Colleges are the engine of our economy, for many people they are the second chance in education, or the first chance that they never had.
"But even if a young person does make it to college under the SNP, far too many don't complete their course.
"A 'sacred responsibility', that is how the First Minister described her responsibility to every young person in this country.
"Well they are being held back by our First Minister. It is harder to get into college under the SNP and if you get in, it is even harder to stay there."
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Ms Dugdale raised the issue as Audit Scotland published its annual review of colleges.
It found a drop in the number of full-time equivalent (FTE) students from 2014/15 to 2015/16.
Audit Scotland also noted FTE student numbers at "incorporated colleges" - the vast majority of colleges - were at their lowest level for almost a decade.
The Scottish Government has disputed some of the figures used in the report.
Since 2012/13, it has set a national target for the colleges to deliver a specific volume of learning.
Audit Scotland found the sector exceeded the target in 2015/16, with 1,752,536 credits achieved against a target of 1,689,431, but performance has declined since 2013/14.
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Nicola Sturgeon said: "One of the key findings... is that the percentage of full-time equivalent students successfully completing their course actually increased in the last year, according to Audit Scotland.
"So what we have is colleges exceeding the national target for learning, more full-time equivalent students successfully completing their course, the vast majority of students saying they are satisfied with their college experience, and more than 80% leaving college with a qualification and going into further study, training or employment.
"On whatever measure we look at, our college sector, yes it's performing under pressure, but it's performing exceptionally well."
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