While the manifesto promise to introduce classes of just 18 in the first three years of primary was popular with teachers -- and many parents -- delivery has been beset with problems.

Rather than legislate to enforce class sizes, the SNP chose to rely on the concordat agreement with local authorities, which charged them with making year on year progress “as quickly as possible”.

However, as The Herald revealed last year, the only class size underpinned by the law is 30 -- contained in regulations passed in 1999.

That meant local authority attempts to reduce class sizes by capping entry to P1 were easily sidestepped by parents using placing requests to get access to a school.

As a result, class sizes in popular schools started to go up, rather than down, and any attempt to introduce a Scotland-wide policy on class sizes was in tatters.

Today’s announcement by the Scottish Government that it plans to amend the current regulations to introduce a new maximum class size of 25 in the first year of primary should go some way to address that.

From now, local authorities receiving a high proportion of placing requests into popular schools can at least hold the line at 25.

This should also be an achievable target for most local authorities because, as statistics published in February show, only 6% of Scottish pupils are in P1 classes above this figure. By contrast, only 13% of pupils in the first three years of primary school are in class sizes of 18 or below.

However, opposition parties are likely to have a field day with the announcement, with many already suggesting the move is tantamount to an admission that the target of 18 is undeliverable.

In an interview with The Herald, Ms Hyslop counters that by arguing that the change to 25 signals the beginning of a more robust approach by the Government.

“You cannot go down all of a sudden from 30 to 18 and the progress we have made in getting these classes down to 25 is very significant and that is why we need to protect it in law,” she said.

“It is too soon to legislate for 18 in the first three years of primary because local authorities are moving towards that target, but this is a short-term measure which will act as a stepping stone to stronger regulation of class sizes more generally. We are conscious that we may need to legislate for 18 at a later stage, bearing in mind the experience we have had with moving to 25.”

Whether Ms Hyslop’s stated aim of delivering class sizes of 18 is a realistic one -- as many dispute -- other significant issues will have to be dealt with if it is to be realised.

One of the main mechanisms for delivery was the retention of teacher numbers at 53,000 to allow schools experiencing falling rolls to bring down class sizes. To help this strategy, the Government has been training hundreds of additional new teachers.

In reality, however, local authorities faced with lower pupil numbers have simply cut staffing, putting class size reductions to one side and leaving many newly-qualified teachers without permanent full-time jobs.

Ms Hyslop told The Herald she was frustrated by this turn of events -- and blamed local authorities for not spending money on new teachers -- but she refused to criticise the concordat agreement which allows greater freedom over spending priorities.

“We know that, during the recession, local authorities have not been able to replace retired teachers at the rate we wanted so the progress in reducing class sizes has also not been at the rate we wanted,” she said.

The other issue still outstanding is whether or not the pursuit of class size reductions -- particularly in the current financial climate -- is the best way of improving Scottish education.

Most researchers agree there is a relationship between small classes and better pupil attainment, but others point to the fact that there is no evidence that class size reductions raise the attainment of all pupils in the long term.