Forkful - firstly, just because someone happens to teach RE at primary doesn't mean they are specialist, or that they have any religious affiliation. Why do you assume that primary teachers are Christian?
Teaching adults is very different to teaching children, especially teenagers, as I said, they don't always listen - I know, I have one and have taught thousands.
I made the point that 'SACREs are indeed very local, I have taught in Plymouth, Devon and Cornwall, and Cornwall has it's own SACRE, as does Plymouth (Unitary authority) and Devon. Within those places there is certainly not a wide range of religious beliefs and the SACREs make great efforts to ensure that the syllabus encompasses different religions to ensure that the kids are aware of diversity.'
The comp I taught at in Cornwall was either all Christians or non-believers, there was religious diversity between Evangelical, Methodist or CofE, but that was it. Cornwall is a large and predominantly white and rural county. The whole point of local SACREs is that they have a local input into what is learned and can provide a balance, so in Cornwall, you learn about Sikhism for example at KS2 and the other non-Christian faiths in KS3. It means the syllabus can be tweaked and there is space within the syllabus to teach a unit of our own choosing.
I far preferred the Plymouth RE syllabus to the Cornish one for example, so there is a difference.
If you look at what used to be the Standards site it has lots of Schemes of work and levels there for KS3 RE, as Charles Clarke was very supportive of RE, but didn't want it to be NC.
If you read this media.education.gov.uk/assets/files/religious%20education%20guidance%20in%20schools.pdf it might explain the SACREs better.
As for collective worship, once they get to secondary, it really doesn't happen; you might get an inspirational reading to reflect on, but the Methodist preacher only came in twice a term, and we had assembly twice a week.