The Scottish Government should "stay the course" with its education policies and "tolerate" the slow progress, international experts have said.

Scotland's school system is in a "strong place", according to the International Council of Education Advisers (ICEA) who praised investment in early years education which they believe will improve attainment in the future.

Following a meeting with government officials, Professors Pasi Sahlberg and Alma Harris said they had conveyed a message of "encouragement to stay the course" with education policies and investment.

Commenting on the state of Scottish education from an international perspective, Prof Harris said: "It's doing everything that we would expect a high-performing system to do; it has all the right components, it is investing in the right places.

"We're not seeing that huge leap in performance but what we are seeing is incremental growth.

"As a council, we're very confident that incremental growth bodes well for the future and the focus on equity and excellence is without question the right focus."

Professor Pasi Sahlberg added: "Improvement in the education system always takes time and somehow the leadership needs tolerate the relatively slower progress than expected that many people would want."

Last year's Pisa (Programme for International Student Assessment) statistics, which record the performance of 600,000 15-year-olds from across the world, indicated that Scotland had seen no improvement in science and maths, but an increased score for reading.

Addressing concerns about the declining number of nursery teachers - raised by Scottish Lib Dem leader Willie Rennie at FMQs - the education experts both stressed the importance of having teaching by qualified people from an early age.

Referencing the education system in his homeland of Finland, Prof Sahlberg said: "The direction has been towards requiring early childhood teachers and educators to hold an advanced academic degree just like primary teachers and all the others.

"It's wrong to think that the smaller the children are, the less education the teachers need.

"In Finland, for example, we think exactly the other way around: the younger the children, the more education the teachers and people who work with them require because it is a complicated and complex setting to work."

Prof Harris added: "That's a very complex stage of education and all the evidence would say it's the most important because that's where children start to diverge and where equities and inequities play their part, so investment in this area is very important."

However, she welcomed the government's pledge to increase free nursery education and said: "The investment in early years' provision is not just laudable but is a major platform for a return on investment in the future.

"Research tells us that if you invest in early years, you will see performance improve."

Prof Sahlberg also suggested that mobile phones are having a significant negative impact on schoolchildren, suggesting that Scotland academic performance could improve if it were possible to cut the number of hours people spend with technology and looking at screens.

"There is no question about whether this has a negative influence on young boys and girls' ability to learn," he said.

"Most of the things that we should be doing with parents and the schools and everybody are the things that have nothing to do with the school education system.

"It's not about curriculum or teachers or leadership or structures, it's something that we parents - together with our children - have to stop and say something is happening that is making not only learning in school complicated and difficult, but many other things."