Just before the holidays, the TES reported on research from the DfE that suggested that there is no discernible effect of non-specialist teaching in science.
I’ve been a science teacher for over 20 years now but because of my setting, I find myself teaching AQA Additional Science for the first time ever. This means I’m having to teach some content that I’ve never taught before in mainstream or special education. The amount of time I have spent prepping these lessons is considerably more than I usually spend as I have had to do plenty of research as I go. Fortunately, there is a wealth of support available and combined with the fact that my students have target grades well below a C they are unlikely to be affected by my lack of subject knowledge.
I do a lot of background reading so that is likely to influence my teaching, as is my willingness to go the extra mile as well. There is overlap between the disciplines of science so I suppose that stands me in good stead but I wouldn’t like the thought of facing a group of top set science students without the appropriate science knowledge to draw upon.
One certainty is that we are going to have a lot more data to draw on in the not so distant future as the number of physics and chemistry graduates entering teaching continues to fall. I also wonder if I should be suspicious these research findings are released at a time of teacher shortages?
For those readers who would like to read the research paper you can find it here.
Fiendishlyclever 
From what I remember, Hattie’s meta-analysis showed a similar lack of correlation between degree and outcomes.
I’ve been in your situation before. Planning is certainly more time consuming and challenging. However, wasn’t that also the case when we taught Physics for the first time?
A-level is a different ball game. My physics degree is definitely useful when teaching a-level. Not sure it’s a massive help with gcse though…