First minister Nicola Sturgeon has conceded that performance in maths and science is "not good enough" after she came under fire over Scotland's performance in the Pisa international rankings.
Scottish Conservative leader Jackson Carlaw said international data showed performance in the two subjects had "never been lower".
The 2018 Programme for International Student Assessment (Pisa) statistics, which were released this week, showed that while reading had improved since 2015 (from 493 to 504 points), Scotland recorded a mean score of 489 for maths, down from 491, and 490 for science, down from 497.
Pisa results 2018: What happened in Scotland?
Ms Sturgeon said independent statisticians regarded performance in maths and science in Scotland as "stable".
But Mr Carlaw, speaking at First Minister's Questions yesterday, said science had suffered the biggest drop since 2003, adding: "Just one country out of 40 has seen standards in science fall further since 2006.
"And in maths, Scotland has experienced the fifth-biggest fall."
Mr Carlaw said: "I welcome the figures in reading, but it is a little bit like people celebrating the fact they have just had their kitchen redecorated when the front two rooms in the house are on fire."
Maths and science results 'stable'
He accused the first minister of being in "denial", quoting Professor Lindsay Paterson, of the University of Edinburgh, on the "disgraceful political spin" the government had put on the figures.
He said: "Nicola Sturgeon's unwavering focus has not been on improving our schools but on forcing another independence referendum on Scotland."
Ms Sturgeon said that "compared to the last Pisa study, the performance in science and maths, according to independent statisticians, is stable".
But she added: "That is not good enough in my view."
The first minister said: "We want to continue with the efforts to see significant improvements in maths and science, as we have seen significant improvement in reading performance recorded in the most recent Pisa study."
She said efforts such as the Scottish Attainment Challenge and Pupil Equity Fund were leading to an improvement in schools, arguing: "What we are doing is working and we will continue to bring the same focus to maths and science as well."
Ms Sturgeon said: "I am not standing here saying the performance in maths and science is, for me or the Scottish government, acceptable, I am not saying that in any way shape or form.
"But after we saw a significant decline in this study, we have seen a performance that has stabilised, and we now intend to bring to bear initiatives and interventions that will see a similar improvement in maths and science to the improvement we have seen in this survey in reading and literacy."
Highlighting other measures of educational achievement, she said: "When we took office less than half of pupils in Scotland left school with a Higher qualification, now almost two-thirds leave school with a Higher qualification.
"When we took office, just over 20 per cent left school with the gold standard of five Highers. That is now over 30 per cent."
Ms Sturgeon added: "I don't think that is job done but that is an indication of the focus and the progress we are and will continue to deliver."