Startail - not sure where your argument fits in? How do you know the IT tech would teach your dcs better? Granted, the supply sounds crap, but just because a person is technically qualified diesnt mean they can teach children & young people.
Itchy I like the letter - very well reasoned, unhysterical and clear. However, like Start I object to the line about only using qualified teachers. I think there definitely is a case for using "unqualified" teachers, particularly for specialist subjects such as IT, languages, music etc. The private sector have been employing "unqualified" but excellent teachers for years.