Hi I run an service to support families at Mediation and Tribunals. I always recommend trying with mediation, if parents can find an additional piece of evidence they can then ask for a reconsideration. I also ask the LA what else they would want to see in order to overturn the decision. I have also gone to mediation with a list of outcomes, such as the school to agree to get an EP in or a SaLT assessment. There are sometimes ways in which they can also support by engaging services such as outreach or specialist teacher involvement. The other things to consider if the LA have up to date evidence of provision map, it can then be argued that the school are currently meeting a, b, c, and d, as on the plan, but not meeting r, s, t, x, y and z, which is well documented in professional reports, but not able to meet due to funding etc.
In terms of Tribunal, make sure parents are aware they will need the mediation certificate, which they can get regardless of whether they choose to attend mediation. The form they require is a SEND 35a for refusal to assess or SEND 35 for refusal to issue. Current dates are coming through for April next year, so if they overturn it at mediation then try to.
Hope this helps. Please feel free to ask any questions happy to help. x