Pressure on schools to show improvements in literacy and numeracy after the introduction of controversial primary testing will lead to teachers rigging the system, an expert has warned.

Professor Andy Hargreaves, an international expert on school assessment and an adviser to the Scottish Government, said "cycnical" methods were used by teachers across the world to inflate test scores if they felt they were being judged on them.

Underhand methods to get quick results could include testing pupils without preparation in one year and then testing pupils the following year at the end of term, he said.

Mr Hargreaves told the Scottish Parliament's education committee: “If there is undue pressure from Scottish Government or local authorities to drive results up in a short period of time to demonstrate success ... then that pressure will lead teachers to do strange things.”

Mr Hargreaves, who works at Boston College and is visiting professor at Ottawa and Stavanger universities, said Scotland's plan initially was to have a "high-stakes standardised test".

However, he said members of the International Council of Education Advisers had warned this "would have all kinds of negative impacts on teaching and learning".

He described the current system of Scottish National Standardised Assessments as "not at all high stakes" although he said it was at risk of becoming "medium stakes" - which could result in schools coming under "undue pressure" to raise performance levels "over a relatively short period of time".

The tests for pupils in P1, P4, P7 and S3 were introduced by First Minister Nicola Sturgeon following concerns over falling standards of literacy and numeracy.