If vocabulary lists are taught properly they will benefit any child in English, regardless of their age and the outcome of school entrance tests.
Some sample advice from tutors is to pick 3 - 5 words a day. They can be stuck on the fridge, a kitchen cupboard - anywhere. The child should then put each word into a meaningful sentence at least 3 times and if possible use the word as many times as they can that day.
Decline: "Thanks Mum, but I'm full now, so I will decline the offer of any more food."
Consent: "I will consent to tidy my room once I have finished watching this programme."
It may sound very formal in terms of today's language and "txt spk", but this very useful post from Patricia highlights why that may be: viewtopic.php?f=38&t=7110&start=10
The vocabulary in 11+ tests tends to be rather "old fashioned" and that can be challenging for children who have not read books from different eras.
Hope that helps.