A Start with good practice in your own school, or in a local network of schools. Can you identify year groups where children with special needs seem most engaged and most successful? What is it about the way teachers in these classes plan children's learning experiences that is working well?
You will probably find that the learning experiences are broad and rich, enabling children to apply their literacy, mathematical and ICT skills in meaningful cross-curricular contexts, and providing opportunities for every child to succeed. Learning is likely to be multi-sensory and children will often work in collaborative groups, using plenty of talk and alternatives to traditional written recording.
Once you have identified what is working you will want to think about how you can enable other teachers to learn from what colleagues are doing well.
Making changes isn't easy when teachers have established ways of doing things. Conventional training alone may not do the trick, so your Senco may need to follow up with coaching for colleagues.
The Senco should jointly plan a week's work with each teacher, co-teaching some of it and then reflecting with the teacher on what went well. Putting ideas like this into your disability access plan and linking this to the school development plan should make sure you get some dedicated time to help everyone develop a more accessible curriculum.