Members of the EIS, NASUWT, SSTA and the AHDS trade unions are taking part in the action in a dispute over pay.
Unions rejected a 5% increase, arguing for 10%. The offer includes rises of up to 6.85% for the lowest-paid staff.
The Scottish Negotiating Committee for Teachers (SCNT) is meeting to discuss the pay options.
The committee brings unions, the government and councils together to negotiate.
The EIS said it hoped the SNCT meeting, which was called at the request of the unions, would advance discussions towards a new offer.
But EIS representative Des Morris, chair of the teachers’ side of the SNCT, said the strikes would proceed in the absence of an improved deal.
Last week, the Scottish government said there was “potential scope for compromise” following a meeting with teaching unions.
Education Secretary Shirley-Anne Somerville, left, said the talks on Friday were “constructive and helpful”.
She added: “We are open to considering options to resolve this dispute through the SNCT.
“I recognise that any deal must be fair and affordable for all concerned, given the unprecedented pressures facing Scotland’s budget.”
Local government body Cosla said there was no additional funding available for an improved pay deal.
Cosla’s spokeswoman for resources, Katie Hagmann, said: “I look forward to maintaining constructive and proactive dialogue, which considers all options available, so that we limit any further disruption for pupils, parents and carers.”
The industrial action follows the biggest Scottish teachers’ strike in decades in November.
Teaching unions in England and Wales are also balloting members over pay.
Most state school teachers in England and Wales had a 5% rise this year, and many teachers in Northern Ireland have been offered 3.2% over two years.
Unions argue that with inflation at 10.7%, these increases amount to a real-terms pay cut.
Scottish Liberal Democrat education spokesperson Willie Rennie MSP, right, today compared the Scottish Government to, “the lazy student who repeatedly submits their homework late.” He made the claim as the government took no action to bring an end to the strikes over the festive season.
Mr Rennie commented: “This week’s strikes threaten enormous disruption for pupils but the Scottish Government took no action for weeks to bring them to an end.
“They are like the lazy student who repeatedly submits their homework late.
“Teachers have seen class sizes rise and classroom support plummet, a direct consequence of the years of neglect at the hands of the SNP.
“The Scottish Government needs to step up the effort to resolve the strikes.”
Top of page picture: Labour MSPs Jackie Baillie and Paul O’Kane supporting the teachers.