General election: Jeremy Corbyn to visit Cardiff
Jeremy Corbyn is to visit the constituency of Cardiff North later on his first general election event in Wales since the poll was declared.
Labour is hoping to recapture the marginal seat from the Conservatives after losing it in 2010.
Shadow Welsh Secretary Christina Rees said her party is the only credible alternative to the Tories.
But Welsh Tory leader Andrew RT Davies claimed the Welsh Labour team would be "gritting its teeth" during the visit.
The visit comes after Mr Corbyn said children were being crammed "like sardines" into "super-sized" school classes in England, as Labour focused its general election campaign on education.
But the Tories called the comments "a massive own goal", saying the Labour-led Welsh government had overseen increases in class sizes in Wales.
Education in Wales is devolved and Liberal Democrat Education Secretary Kirsty Williams has announced a £36m fund to reduce infant class sizes in Wales.
Mr Corbyn will say: "We're fighting in Wales to give everyone a better standard of living, to build on the excellent record of Welsh Labour in power here in the National Assembly of Wales."
Welsh Labour leader Carwyn Jones said he will be meeting Mr Corbyn in Cardiff later. He was initially not expected to be attending the event.
Ms Rees will be with Mr Corbyn on Friday and said: "The Labour party is the only credible alternative to the Tories".
"Like the SNP, nationalists in Wales claim to be progressive but at the Welsh assembly Plaid Cymru members have voted against investment for hospitals, schools and homes," she said.
Labour said this was a reference to a decision by Plaid Cymru AMs to vote against the allocation of extra cash to the Welsh budget for 2016/17 - although it had supported the budget for 2017/18.
The Welsh Government was criticised at the time for not fully explaining why some of the extra spending was needed.
But Mr Davies said: "After nearly two decades in government, Labour's record is a smorgasbord of failure evidenced by Wales having the worst-performing education system in the UK, the lowest take-home pay, and the longest hospital waiting times."
Jonathan Edwards, Carmarthenshire East and Dinefwr Plaid Cymru MP, said: "Given the current weakness and chaos plaguing Labour, the prospect of a UK Labour government is a complete fantasy."
Meanwhile Rhondda MP Chris Bryant said he was "fully supporting" the leader, despite being a vocal critic when he was voted into the role.
Analysis by BBC Wales political correspondent Arwyn Jones
When it comes to class sizes it is difficult to make a direct comparison with the figure in England because records there are kept of pupils in classes of 36 or more, which is not publicly available in Wales.
There are 4,568 junior pupils - 3.4% - in Wales taught in classes of 31 or more last year, known as "unlawfully large classes".
The number has more than doubled since 2013 when it was 1,688 - 1.3%.
There are circumstances where a class may have more than 30 pupils, which are called "exemptions".
Last year, 12,711 pupils were taught in such classes, 9.3% of the total, up from 8,082 in 2013.
However, Welsh Government pointed out that between 2013 and 2016 there has been fall of 41% in the number of infant pupils in unlawfully large classes.