Teacher warns Nicola Sturgeon: Curriculum for Excellence is utterly failing children in school

He appealed to her to listen to teachers with direct experience of how pupils are being negatively affected by a system which he claims is not fit for purpose.

He also warns of an "unprecedented decline in the organisation and standard of Scottish education" over the six years since the controversial Curriculum for Excellence was launched, adding: "The system as it stands is not fit for purpose.

"It is demoralising, hobbling and utterly failing the children in our care; as well as lowering attainment and widening social inequality in our pupils."

Mr Wilson, who has been a teacher for 16 years, is a former SNP member and 'Yes' voter. Since posting the letter on his blog, it has been viewed by more than 12,000 people and shared hundreds of times on social media.

He said he initially wrote it in response to growing frustration at the repeated changes to course structures and pupil outcomes targets, which have meant he has been unable to teach the same course for more than a single year at a time.

However the Edinburgh-based father-of-two opted to publish it after Trinity Academy in the capital was last week forced to appeal to parents to help teach maths classes after failing to find teachers to fill vacancies.

Scottish Conservative shadow secretary for education, Liz Smith, said the letter shows the extent of concern over the delivery of the Curriculum for Excellence. "This letter is a serious warning to the SNP. After months of dithering they need to act," she added.

"This teacher speaks for many when he highlights the lack of clear direction within the Curriculum for Excellence and the lack of academic rigour in far too many subjects, all of which is having a devastating effect on teacher morale.

"The Scottish Conservatives have been arguing for some time that the Curriculum for Excellence needs proper direction, clear purpose and much more focus of basic literacy and numeracy and core subjects which are so important to the job opportunities of all our young people."

Scottish Labour's education spokesman Iain Gray said: "It was less than two weeks ago that Nicola Sturgeon launched her Programme for Government claiming that education was her top priority. Yet again, that claim lies in pieces.

"The last week has been disastrous for the SNP, with another head teacher reduced to writing to parents asking for help after his school was unable to fill Maths teacher vacancies.

"Now, we see a letter from a teacher who is a professed SNP supporter, slating the Nationalists record on education. After a decade of SNP government, we have 4,000 fewer teachers, bigger class sizes and hundreds of unfilled vacancies." The state of Scotland's education system has come under increasing pressure with signs of an academic slump and concerns over disillusioned teachers leaving the profession.

In March, a shortage of Steam teachers led to Blairgowrie High School appealing to parents to come forward to help teach their own children, while figures last month suggested Scottish schools had as many as 500 vacancies ahead of the new school year. A total of 20 councils reported 404 unfilled posts evenly split between primary and secondary schools and 12 other local authorities are trying to fill around 100 positions

The latest Pisa results show there are 14 countries rated better than Scotland in mathematics, 13 in reading and 12 in science. In 2006, those ranked higher were nine, six and six respectively.

In his letter, Mr Wilson says the current conditions teachers are labouring under are so gruelling that they are starting to "hate, dread, stress over and now depart a role we loved so much".

Changes to his own subject, Biology, have left it "unreasonably difficult, lacking opportunity for practical activities, far too prescriptive, overly concerned with inconsequential minutiae and extremely content-heavy."

While teachers struggled to keep up with alterations to exam requirements, an 'elitist' structure was developing with pupils who might have previously attained a Standard Grade 3 or even 2 level being left with little hope of passing or even being able to sit the final exam.

A lack of value placed on the National 4 qualification meant pupils were classed as not academic "and sat to one side as the certificate kids get taught how to pass the exam," he added. "This elitist approach is counter to any good teacher's desire to provide the best opportunity for our children to succeed.

"I didn't become a teacher to tell a portion of my kids they aren't good enough to sit an exam."

He called on the First Minister to "utilise the resources, the well of skills and experts you have at your disposal, and please, please save our education system from the disaster that is CFE."

A Scottish Government spokesman said: "The Scottish Government values teachers for the vital work they do educating and inspiring our young people. We have made a commitment to tackle bureaucracy and address excessive teacher workload. That will continue to be a key theme of our bold education reforms which also include headteachers being given more power to make decisions in their schools to improve education and more money to make the changes needed.

"As the OECD's independent review showed, Curriculum for Excellence (CfE) is the right approach for Scotland and provides a solid foundation on which to transform education nationally, with the latest exam results and statistics on positive destinations demonstrating that CfE is successfully meeting the needs of young people. Changes to National Qualifications were welcomed when announced last year, with the removal of unit assessments freeing up time for teachers to focus on learning and teaching."