While I totally agree with Mr Purcell that poverty isn't an excuse for failure and that there are a small minority of teachers who require major support, such a sweeping assumption cannot go unchallenged.
Deprivation is clearly a huge, though not decisive, factor in educational attainment. Many children from poorer backgrounds do well at school and thrive under the supervision of loving parents and efficient teachers.
However, research has shown repeatedly that children who live with deprivation are more likely to struggle in school than those living in higher socio-economic groupings.
The Literacy Trust, hardly a bastion of socialist malcontents, has published research findings for a number of years which clearly illustrate the link between poverty and attainment.
Is it so surprising that, on average, a child who lives in a home with internet access and shelves full of books does well at school? In the case of Glasgow, the evidence of deprivation and social inequality is overwhelming. The Scottish Executive's own figures suggest that 16 of the country's poorest council wards are in the city. It makes depressing reading and doesn't reflect well on 80 years of one-party control of the city.
The Scottish Executive also admits that 25 per cent of Scottish children live in poverty (260,000 children). The charity One Plus states that between a third and a half of Scottish children will spend at least part of their childhood in a one-parent home. Of these 151,000 lone parents, 52 per cent will be on income support.
All of this leaves me feeling that Mr Purcell should temper his remarks about "failing teachers" by praising the vast majority who do wonderful work, often in very trying circumstances.
He has much praise to offer Glasgow's "great team of headteachers" and states that he will fully back their decisions if they think that staff should be removed. While I agree that heads are indeed well placed to spot struggling teachers, who in turn is well placed to spot struggling heads?
Much research points to good leadership as a vital component in successful schools, yet HMIE tells us that as many as 15 per cent of the leadership in Scottish schools is weak.
As a teacher in Glasgow, I see much wonderful work going on in our schools.
A host of initiatives have improved standards and made the learning experience much more exciting and effective for our children.
New school buildings are going up and there is a general optimism about the future. Mr Purcell himself has been closely involved with the laudable programme of building modern, community-based pre-12 campuses.
Is it asking too much for some of our successes to be exposed to the public gaze?
Patrick Marrinan Cumbernauld Road Riddrie, Glasgow