Different statistics and researches can give contradictary results.
Here's an extract from an NFER reseach document :'The impact of selection on pupils performance'
The research suggests that:
• the most able pupils perform just as well, if not better, in comprehensive schools
• the least able pupils perform slightly better in secondary modern schools
• the impact of different school types is most strongly felt in the overlapping ability
range (average to above-average).
It seems therefore that selective systems obtain good results, particularly at key stage
3, because the grammar schools are remarkably successful in enhancing the
performance of their least able pupils – the ones who gain their grammar school
places by a relatively narrow margin. There is a common view that ‘borderline’
pupils fare better at the top of secondary modern schools, rather than ‘struggling’ in
grammar schools; our research completely contradicts that assumption.
http://www.nfer.ac.uk/publications/othe ... agen01.PDF
Of course, what applies to a group of children may not be true for each of them individually. Children who lack confidence may perform better in the top group of upper, whilst those who respond well to being more stretched
may do better in grammars.
As for appealing, I think that this is different to the 11+ preparation in the way that the stress and the work falls on the parents, not on the children. In many cases, the child doesn't even need to be aware of it.
In my opinion, if you think that your child would do better at grammar, go for it.
But that said, my son's friends who have started at secondary are happy and loving it.