Tens (and units) nervous headache!
A The very fact that you are not defeated and seeking a solution suggests to me that you have a great deal of patience and are more likely to be an excellent TA. What you must realise is that it takes time to pick up the "tools" of the trade.
We learn from our pupils all the time and their lack of understanding quite often leads to us discovering a new way to approach a topic. Teaching is not always an easy task, but over time you will "collect" lots of strategies to help support pupils like yours.
For example, I had a similar problem teaching a pupil online. I couldn't have a manipulative in front of us so I had to think of an alternative.
Using PowerPoint, I first created numbers as pictures, using ten sticks and unit squares for the various numbers. I could show the PowerPoint slide as a background image on a virtual interactive whiteboard, so we could write and draw over the slide.As we could both write on the whiteboard via the internet it was easy to demonstrate and discuss the different numbers. I began with 46. I wrote a "T" (tens) above the four lines (of 10) and a "U"
(units) above the six squares. I asked what number was under the tens. She told me 40. I wrote a four over the sticks and a zero in the units, as you can see in the second diagram, telling her that I hadn't yet counted the units, so I didn't know what number needed to go there. I then asked her how many unit squares there were (I drew an arrow pointing at the units as I spoke). She answered "six", so I wrote a six inside the zero using a different colour so that it was easier to see. I then cleared the screen and wrote the number 46 over the blocks. We worked through some examples together until she was able to just write the number. Over-writing the zero with the units seemed to be the "wow" moment. This is why I think that although place value cards are useful, writing this yourself has more power.
I then gave her some problems where she had to make the number by choosing the correct sticks. We then explored the number as addition sums in a line (40 + 6 = 46) and relating this to a number line. We followed this by setting the sum out vertically.
As follow up I directed her and her parents to some games on the internet for her to practise: matching numbers and pictures at www.ictgames.comsharknumbers.html; moving bricks to make the number indicated at www.learningbox.comBase10BaseTen.html; and choosing the tens and units to make the target number (as in my example with 46) at atschool.eduweb.co.uktoftwooddinoplacevalue.html.
I suggest you try this with your pupil - I would be interested to know how he gets on, and if you copy the slides I have sent onto acetate then they can be re-used with other pupils. If anyone else would like a copy of the PowerPoint please email me and I will send a copy. This exercise could be done on an interactive whiteboard with the whole class.
Today on a visit to St Paul's
I met a girl who puts up walls
A defence against failure
"Me? My name is Hannah"
Then in her offhand manner
"I'm really not interested!"
The dance timetables are organised
But Hannah's tutors are surprised
"I don't understand time"
"Look there's a clock face there"
They point, she doesn't care
Because it's maths
"There is just a chance
If you learnt through dance
It might make sense"
Almost with a sigh
She'll give it a try.
It might help.
Through kinaesthetic creation
Now this lady in town
Has her defences down