You should be able to request anything, but your requests don't have to be followed. My understanding is that legally, the teachers have to do something to try to help him achieve his goals, but they don't have to do the thing that you want. If you can show data that the thing they want to do is not working for your son, you can get them to change it, but again, they have the discretion about what to change it to.
Did the case worker agree to go over daily assignments with him when you asked? What did s/he say when asked about the empty notebook?
If the teachers don't already have assignments posted online, I think you're going to find it very difficult if not impossible to get them to do that. Better to come up with a system that is more suited to dealing with a single child - for example, email him assignments (and then you have to make sure he checks his email every day).
