Hi Montues!
I set up an account so that I could reply to you.
In my (by now bitter) experience, mediation is basically a tool for the LA to screw nice cooperative parents trying to get their child's needs met. I went down this route twice and had to get an expensive (but effective) specialist lawyer to even start to get get the LA to do what it should have in the first place. First they refused to assess, then refused to issue Satetement/EHCP. Got a lawyer, took them to Tribunal, the LA conceeded once the Tribunal agreed to hear the case. Very cynical.
Dragging things out and dragging you down saves them money.
If you cannot afford specialist legal advice (with proven track record), then get in touch with SEND charities/orgs to see what you should be doing yourself. Pay close attention to deadlines. Are you still within deadline to appeal to Tribunal for refusal to assess? If yes, do this ASAP (check what effect being in mediation has on this).
If you can afford independent EP then get your boy assessed - preferably by one with lots of Tribunal experience (this is where specialist lawyer is handy, since they have a list of people they work with). Try to work out what other assessments he needs, including medical ones, and get him on the waiting lists.
Put up your question on the SEN forum if you have not already. There are a lot of people there with many years of experience, and may be able to point you in the right direction/ask pertinent questions.
Best of luck getting what your child needs (and has a right to!).