Made me cringe a bit, the emails thanking them for teaching their child!
That’s a bit harsh. 
I emailed several of my y11 dc’s teachers to thanks them, but I did it as soon as the school announced they were closing in March, and before the announcement that the grades woukd be based on teacher assessment rather than exams.
It had nothing to do with my child’s grade prospects, and everything to do with the fact that these teachers had really gone the extra mile to support and engage my child, and it was disappointing for the dc and the teachers to not be able to see it through.
I had a very emotional reply from one of the teachers, so I know it was taken in the spirit in which it was intended. :)