So they have refused to carry out an EHC Needs assessment. As 10brokengreenbottles says don't bother with mediation (our solicitor advised us not to bother too).A lot of LAs use mediation as a delaying tactic, and then parents still end up having to appeal, only several weeks further down the line, which is not in your child's best interests.
The requirement is only to consider mediation, not to actually participate in it, although you will need a mediation certificate to register the appeal.
Just ring up the number on the refusal letter the LA sent you and ask them to issue the certificate.
IPSEA has complied a Refusal to Assess pack here:
www.ipsea.org.uk/Handlers/Download.ashx?IDMF=b006465c-2b25-4e28-839b-6417bfbb2da0
No idea what a "Way Forward " meeting is, but it won't be an official mediation meeting. I suspect it's just a means of distracting you and fobbing you off (aka another delaying tactic). 
I would cut through the crap and just tell them you will be appealing as it is clear your child may have special educational needs (communication difficulties extreme sensory needs , and anything else that is a problem eg poor social skills , delayed development etc) and that it may be necessary for SEN provision to be made via an EHCP. ( they can't possibly know whether or not he needs a plan until his needs have been investigated by professionals who will advise on the support and provision he needs).
This test is set out in the law (Section 36(8) of the Children and Families Act 2014). This is the only criteria that should be considered.
LAs sometimes fob parents off with "LA policy" - policies of not carrying out assessments until children are X number of years behind/school has spent £6000 /school have done this that and the other etc. These policies are all unlawful as LA policy does not trump the law.
Some LAs have a policy (again unlawful) of refusing all requests for EHCNAs until the parents appeal and then they back down.Hopefully yours will too.
Is it possible you could qualify for Legal Aid? Information here:
www.ipsea.org.uk/where-can-i-get-help-with-making-an-appeal