A Level Chemistry is brutal!! But I get your point, other jobs are just as challenging.
By my assessment (reading news and knowing a couple of teachers)
Teachers get:
A standard salary that is more than a UK full time average salary
An extraordinarily generous pensions scheme not available to 99% of the private sector.
12 Weeks paid holiday
They also get
A job that can't be done in their contracted working hours so work an awful lot more such that the holidays aren't always holidays
Stress and high pressured environment
Threats of violence and abuse from increasingly disruptive pupils and even parents.
My conclusion
Teachers deserve a pay rise. They graft like nobodies business and deserve to earn more than the average wage. The NEU demanding 12% in the current climate is unrealistic and a slap in the face to all the hard working people out there whos tax will pay for this as well as the pensions that they can't access. If 12% is desired the defined benefits scheme must cease and a new NEST scheme established to be in line with the private sector.
We must do something about the working conditions irrespective of the salary discussion. It is not fair or sustainable.