I already had 80% of the qualification to do the assessments through my postgraduate studies, so I just had one 3-month postgrad paper to do and then a year of training and supervision with the Learning Disabilities Association here. It's not a program as such, as they only train up a few selected people each year. If it's something you're interested in, Educational Psychology or a Masters in Education is worth looking into or contact your local Learning Disabilities Association.