I am the UK Sales Manager for a company that provide language lab solutions. Labs can be supplied for wireless networking, classes without PCs and for laptops but there is simply no way to run an effective lab over Citrix.
Language labs may be a minor consideration but do take this in mind when you decide to move a school over to a thin client environment.
There is a product working at Taunton School but my understanding is that this is less than ideal and that even the staff would like an alternative.