Following on from CXC's point regarding the fact that the VAT would not be a cost to your VAT-registered client, if you were to go down the road of providing VAT-exempt supplies, you would end up having to make an adjustment on your own VAT input credits...
e.g. say 20% of your turnover related to VAT-exempt training, and therefore 80% of your turnover was derived from VATable supplies; then you would only be entitled to an input credit for the 80% of your overheads (e.g. light/heat, phone, motor etc...) that relate to the taxable activity.
As you can see, it all gets very messy very quickly, so you will be much better off deciding that the type of training services you are providing are not "Vocational training", and just invoice the VAT...