Some might like to consider sending a note of appreciation/commendation to the TA's boss.
Writing things like '..... thanks to X's professionalism, we feel that we have found the one TA we can deal with again and again in the future' sends the message 'we're coming back for more' and also sends a messge to your TA's boss 'keep him/her - and make sure you keep him/her happy if you want repeat business'.
In addition to tipping onboard for Nursery staff - I sent a letter to the Line's Customer Service department saying how 'superb' the staff were. Customer Services wrote back to me saying that they were passing my letter on to the Captain of that ship. Whether they actually *do* or not is another matter. But at least you've done your bit to 'big 'em up' - which stands them in good stead when it comes to promotion time etc.