How To Avoid The Nervous Knee Shaking?

My son failed his driving test again today and from the feedback he received, the key contributor was nerves - he couldn't stop his legs from shaking at the beginning. The examiner suggested he speak to his GP to see if he could recommend something. My son is 18, weighs about 10 or 11 stone and apart from his JME (controlled with Eplim & Lamotrogine) is generally healthy and confident. He (I think sensibly) would not want to look at additional medication just to calm his nerves for the next test but we are wondering what he might be able to do. This was his third attempt and he had similar experiences on his other tests - if he could just avoid the nervous knee shaking I think he'd get his licence!