BBC News has done a great video-report, showing how kids themselves feel about taking the 11+ exam, and the sense of pressure they can experience if too much of a 'big deal' is made of it at home. It's well worth watching as it may help parents figure out how to navigate between being too pushy on the one hand and too relaxed on the other:

http://www.bbc.co.uk/news/av/education-44227979/grammar-school-tests-how-do-children-cope