Yes, as far as extenuating circumstances are concerned, I would say so, if it is the case that he does not have the knowledge of the nuances of English needed for many questions in the test.
Of course, there would need to be alternative evidence of very high ability (e.g. in maths, quantitative reasoning / NVR).
If the school will be oversubscribed, there will also need to be good reasons for wanting a place.http://www.elevenplusexams.co.uk/appeal ... -school#c2
The final point to bear in mind is that appeals for some schools can be much harder than for others.