A business that did not reward its employees for enormous extra hours yet allowed slackers to survive for a few years however low in number would either go bankrupt, or everyone in the organization would get the message that extra work was pointless and change accordingly. Unless it's curing cancer or working with kids or some other noble purpose, people work for money and career. Of course you simply can't "fire" underperformers (children / teachers) so education is not a business and never will be.
That's the issue though. No teacher who actually gives a crap will 'work to rule', because first their kids suffer, and then their employment prospects will too. Not to get all Dead Poets, but people don't go into teaching for the pay. Many go into it to make a difference. If that means doing an extra hour or two to work out how the heck to get these kids up to the next standardised level, or a higher exam grade, then they very often will. Even the ones who don't care know that it matters if they want to keep working in the profession, and act accordingly. If this was business, you'd find a rival who paid overtime. That doesn't work here, for none of the other schools do it either.
In the UK, the government is increasingly treating the process of teaching like a business, while ignoring the fact that underachieving pupils still need to go to school, so have to go to school somewhere. Having to run a successful business, while having little to no control over one of the integral parts of that business, is not particularly easy.
However, under-performing teachers are not kept on the staff of schools in the UK for very long. At one point, that may have been the case, but my experiences recently suggest that it certainly isn't now.
I know you might think of this as simply the ordinary, steady eddie work of teaching, but it's pretty impressive to me! And thank you for your good work.
It is impressive, but it is also expected. If Lindseyman is, as his posts suggest, a Secondary School teacher, then he needs to make sure that his subject isn't out-performed by rival ones. If other subjects get better exam results, and help move the school further up the league table, then they'll be prioritised, at the expense of his own subject.
It's self preservation, professional pride, and actually wanting the kids you teach to succeed. Normally in vaguely equal measure.