Media playback is unsupported on your device Media caption NAHT Cymru policy officer Rob Williams says every school needs to be involved

An overhaul of the school curriculum in Wales is facing difficulties in how it is being put into practice, a committee of AMs has said.

The education committee said some parts of the roll-out of the new curriculum proposed by Graham Donaldson were not "progressing as well as we would expect".

It is intended for the new curriculum to be fully up and running by 2021.

The Welsh Government said it was collectively appraising progress.

Lynne Neagle, committee chairwoman and Labour AM, said: "The important thing is that we keep the whole programme on track to deliver by the overall deadline of 2018 and statutory implementation in 2021."

She added: "My concern is that we get these reforms right."

Prof Donaldson argued that computer programming and IT in all classes should be as important as literacy and numeracy.

His review found that schools should have more flexibility to teach around a central curriculum.

Ms Neagle said the vision from Mr Donaldson was "largely conceptual".

"Whilst it is widely supported, it is apparent that there are difficulties and challenges in translating that vision into tangible implementation," Ms Neagle wrote in a letter to Education Secretary Kirsty Williams.

The letter, written after the committee took evidence on how plans were progressing. said:

Evidence suggested the Welsh Government needed to offer stronger strategic leadership in putting the review into practice

Schools chosen to help lead the development of the new curriculum - so-called pioneer schools - are not clear on what is expected of them

Misunderstandings on the relationship between assessment work and the curriculum - i.e. which is set up first - could prove a risk to implementing the system

That the design of the curriculum should not replicate other countries' experiences

AMs said they were concerned there had been delays in designing the six areas that will form the basis of the curriculum.

So-called strand two - which will see the outline of the curriculum drawn up, was meant to have started last September and completed in June 2017.

The first meetings of working groups to do the work only took place, however, on 17-18 January 2017.

The National Association of Head Teachers (NAHT) told the committee there was "now a need for greater clarity as to what the new curriculum and assessment system will actually look like".

The National Union of Teachers (NUT) said "we are still awaiting the devil in the detail" and told AMs there was a "lack of direction and vision in terms of translating the fantastic vision of the Donaldson review into something tangible".

Image copyright Thinkstock Image caption Summary of the review proposals

Analysis from Colette Hume, BBC Wales education correspondent

This new curriculum heralds the biggest shake up of education in a generation and the first time a Welsh designed and implemented curriculum will be taught in classrooms in Wales and the pressure is building to see if it can be delivered to every school in Wales by the deadline 2021.

Covering ages three to 16, the new curriculum will see all teachers expected to deliver learning in literacy, numeracy and digital competence.

The curriculum will be divided into six areas of learning, from the expressive arts to science and technology.

In November 2015, 68 pioneer schools were chosen to lead the way in developing the new curriculum and more have followed.

But from what schools and teaching unions appear to be telling the education committee, there is confusion about what they are actually being expected to do and how they will help design the new curriculum and assessment arrangements.

There is enthusiasm within the teaching profession for the new curriculum, but both schools and unions are now looking for clear leadership and direction from the Welsh Government on the way forward.

Schools inspectorate Estyn wrote: "After a year of thinking time, it is time to increase the pace of progress."

One of the pioneer schools, Ysgol y Strade in Llanelli, Carmarthenshire, told the committee: "It's fine to get teachers to create this and build it from the ground up, but sooner or later, we need one clear goal, we need one document to say 'this is the model'.

"At the moment, we don't have anything near that."

Gareth Evans, of University of Wales Trinity Saint David, said the letter "reflects the views of many in Wales' education system".

"While there is widespread engagement with the Welsh Government's reform of Wales' national curriculum, primarily through its pioneer schools network, there is underlying concern at the pace of progress and timescale for delivery," he said.

"Those at the forefront of curriculum development have spoken of the need for a guiding framework to support them in their work - and other, non-pioneer schools, require better forms of communication to update on the direction of travel."

The Welsh Government said it was confident that the new curriculum was the right approach and the education secretary would respond to the committee in due course.

"In line with Prof Donaldson's recommendations, as the work progresses we are continuously and collectively appraising progress in order to strengthen implementation," said a spokesperson.