Some thoughts:
1. You could ask the head to OK you doing some “learning walks” around the school (possibly with someone else from the SLT) so that you can get a feel for what is going on.
2. Remember that the SENCO has a critical role to play in ensuring that children with special educational needs and disabilities within a school receive the support they need. Your duties include co-ordinating provision for children with SEN – to do this you need to be able to monitor what provision is being offered.
3. You are also responsible for the IDENTIFICATION of children with special educational needs in the school as well as the TRACKING and MONITORING their progress. You can not do this without being able to see the children in class, talk to teachers and TAs, etc.
Clearly some teachers do not want you to know what they are (or are not) doing to support pupil needs. Are they afraid that you will heap additional work on them? They SHOULD be doing this anyway so would be in breech of their teachers duties. Talk to the Head and SLT and raise your concerns about an apparent culture of secrecy in some classes and insist that they get involved – after all, if Ofsted arrives, they will want to see evidence of this provision being put in place and failure of other staff to do so could harm the school’s grade.
Good luck. Culture change can be difficult in a school!
Hope you get it resolved.
John