The Chartered College of Teaching believes strongly in the value of teacher professional learning. Yet the term encompasses a huge variety of things; CPD can take myriad forms, many of which are explored in our new report on teacher CPD internationally, full of articles and case studies exploring trends, opportunities and challenges.

This variety means that not all CPD is created equal; there is no doubt that its quality and impact varies hugely. So what should teachers (and school leaders) be thinking about when they are choosing what to invest in?

The DfE’s Standard for Teachers’ Professional Development is a good place to start – but it’s important not to oversimplify this and to look at the detail behind the standard, not just the headlines.

Let’s take the first standard – that “professional development should have a focus on improving and evaluating pupil outcomes”. It’s hard to argue that the ultimate aim of teacher CPD should be anything other than improved pupil outcomes. But does this mean that to be worthwhile, all teacher CPD needs to change teacher practice in such a way that it has a measurable impact on, say, pupils’ GCSE results the following year?

It’s not as simple as that. At times, CPD might also provide teachers with the confidence not to change their practice, to resist unevidenced trends or demands that can swallow their time.

One of the ways teacher CPD can have an impact on pupil outcomes in the long term is through the role it plays in teacher retention. For example, an evaluation of the impact of subject-specific professional development for science teachers carried out by Becky Allen and Sam Sims for the Wellcome Trust suggested that it had an impact on teacher retention. An important consideration in the midst of a retention crisis.

When it comes to CPD, it is important not to narrow purpose

Of course, one might reasonably expect that engaging in science teaching CPD would, in time, also improve classroom effectiveness. But improving science teacher retention and thus increasing the chance of a class having a specialist teacher in front of them seems valuable in itself.

It’s worth, therefore, also thinking about teachers undertaking wider subject knowledge CPD, such as a masters in their subject. Strong subject knowledge is a prerequisite for effective teaching, but there are caveats.

It seems to be knowledge of the particular areas being taught that matters, and while a minimum level of subject knowledge is needed for a teacher to be effective, teacher effectiveness does not continue to increase as rapidly above that level.

But given evidence around CPD and retention, and that for secondary teachers a love of their subject is a main driver for joining the profession, encouraging them to continue their subject scholarship seems worthwhile.

Given the investment required in CPD – the cost, associated cover, and teachers’ time – we need to know that such activities are worthwhile beyond simple teacher satisfaction. CPD needs to challenge us, and this can be uncomfortable. Yet without this challenge CPD may risk simply reinforcing existing, ineffective practices.

Potentially worse than that, without quality assurance, a teacher could be supported through a highly engaging course or instructional coaching cycle only to develop a pedagogical approach that is underpinned by very little evidence.

So when it comes to CPD, it is important not to narrow purpose, and to recognise that it has dual aims – improved pupil outcomes, yes, but also teacher satisfaction and retention – and that they are complementary.

We know that teachers become more effective over time, so improving teacher retention should lead to improved overall effectiveness of the profession. Meanwhile, high-quality CPD that leads to improved pupil outcomes will in turn contribute to teachers’ professional satisfaction. So when we support teachers to be autonomous and to select high-quality CPD that meets their needs and will impact on their students, we can achieve two goals at once.