Hello, and welcome!
Your essential reading for this is Section D, here: viewtopic.php?f=12&t=41358
1st, in the review paperwork they appear to have an incorrect school recommendation, stating it as 1:2 when my paperwork says 1:1. Would this have had an affect on the review decision and therefore be grounds worth appealing upon?
It is certainly a point in your favour when seeking to overturn the Review decision. How can the Review have been "Fair" (as in "Fair, Consistent and Objective") when a key piece of information appears to be incorrect? Was the discrepancy noted by the panel? If so, where is the evidence of that? (There won't be any ...)
Whether it is enough to overturn "F, C, O" is less clear. It will depend on how accurate the Head's recommendations were overall (and whether that recommendation was made before the test result was known.) If you can demonstrate to the panel that, in all probability, the incorrect recommendation would have been a significant factor in the Review Panel's decision-making - and you will only be able to do that once you have seen the recommendations - then it is possible that the panel would overturn F, C, O.
(There may be other points you can make about the Review process, as per the link above.)
And 2nd, the reason stated for not being successful in the review is that his low CAT results were consistent with the STTS, indicating my son is not suitable for GS. Even though his CAT scores were low, again these are not consistent with his academic achievements which have been consistently very high throughout KS2.
CAT scores are widely considered to be reliable indicators of academic potential, which presents you with the issue of explaining why they aren't higher. However, appeal panels are trained to understand that CAT scores are not
directly comparable with 11+ scores.
If there is only one set of scores, as is often the case for state schools, the scores might be discounted as less reliable, and the academic evidence considered to be more representative of your son's ability. If, however, there are two or more sets of scores and they are all in the region of the 11+ score, your case would be weakened considerably.
Is academic evidence NOT consistent with CAT scores evidence enough to be successful at appeal?
It very much depends on the strength of that academic evidence and how credible it is. For example, if your son had already achieved Level 5s across the board in Year 5, that could possibly trounce a single set of CAT scores.
I don't know whether to go through the stress of appeal and don't want to if we are unlikely to be successful.
I'm sorry to say that it will indeed be very stressful because you are unlikely to know the outcome of the appeal until June or possibly July. That may also mean that your appeal will need to cover oversubscription if your preferred school no longer has any vacancies. That adds a further layer of stress.
Whether to go ahead with an appeal probably rests entirely on whether the alternative school is acceptable or completely unpalatable to you and your son.
If the Head is approachable, I suggest that you start by asking for sight of their overall Recommendations.