Time yourself writing sequential numbers 1 through X as fast as you can in 30 seconds. And note your results.
Then time yourself writing the alphabet A through .... as fast as you can in 30 seconds.
Now, in 30 seconds, write A1, B2, C3, D4.....
You would think it is easy to do this because you have been writing numbers and the alphabet your whole life, but context switching is hard.
I show my students that cognitive abilities declined significantly with lack of oxygen. I have them do jumping jacks while reciting the alphabet backwards. There is often a 50% decrease in speed when they are working out.
I can recite the reverse alphabet almost as fast as forward without the added stress. While working out I can do it with a10% decrease. This leads me to believe that the additional stress can be compensated through drilling.
That would be one more classroom nightmare for me. The only way I can recite the alphabet is by singing that stupid song I learned in grade school. To do so backward, I would first have to sing forwards until I reached the next 'backwards' token, for each and every letter, so jumping jacks or not it would be at least 50% slower.
Even with the song I sometimes get stuck, but I also have a dyslexic mind and absolute hate any alphabet exercises. I would absolutely hate your class (but not you necessarily) and would spend my time in there counting down the school year to never have to go again.
On the other hand I wrote Z25 (uh-oh) and I couldn't spot my mistake until I had the computer write it down too. All the letters were there. But I wrote down 16 twice and I didn't spot the error even afterwards because I was too focused on the letters.