If you are absolutely certain* that you were parked OK, write a letter of complaint to the Headteacher and copy in the Chair of the school governors.
If you or the car were identifiable in any way from the photo (eg visible registration number, driver's face etc) I would very politely write that you resent the untrue suggestion that you had parked/had stopped/were waiting in a way that contravened any traffic regulations, and that you are sure that the school will understand that you would like an apology and a correction to be printed in the next newsletter. (You can also clearly state that you were identifiable from the photo because other parents have mentioned it to you).
See if that works.
You don't want to go to court for defamation as you'll need access to about £10k in fees before you get out of bed. You just want an apology and a correction. If what you've told us is accurate, I don't see any reasonable school failing to say sorry.
*My wife is a former school governor and my experience listening to her is that very very few parents actually understand the meaning of the no stopping/no waiting signs and road markings outside schools. Don't complain unless you are sure you weren't stopped where you shouldn't have been.
And they haven't offered a speed awareness course either? (Have you done one in the last three years or is this in Scotland?)
And is one of the notices for 34 in a 30? As Man in the Middle says, that ought to be below the level at which they take action.
(And sorry - I don't want to appear preachy - but... there don't have to be any warnings or signs or lines on the road to advise you of the presence of speed cameras. If you get away with an exceptional hardship argument you will need to stick to speed limits in future - whether you know there are cameras there or not. NB Don't know if this applies to you, but most 30 mph limits are restricted roads with a system of streetlighting and don't even need speed limit signs - you are assumed to know this from the Highway Code).
It's up to you if you want to pay £300 you don't owe plus whatever Unicorn Food Tax with no basis in law whatsoever that they will have made up in the Letter Before Claim.
We'd prefer you didn't.
But you have received a LBC so it's make your mind up time.
- post up photos of the signage in the dark that you'll have taken two months ago (post 14)
- post up details of planning permission for their signs you'll have found out after you got onto the council, again two months ago (again post 14)
- also let us know if you agree with Brassnecked's excellent letter or if you'd like to tweak bits depending on what you've found out
- upload the LBC. Some of them are appallingly drafted and invariably contain Unicorn Food Tax which is all useful extra ammo
- also, where are you living now (post 35) and are you comfortable with legal communications arriving at your parents'?
If you look in our PPC Successes thread at the top of the page, you will see 275 times these cheats have been seen off with their tails between their legs (and all had the same "well known legal companies" (ho! ho!) on hand). In reality 275 times is a massive underestimate, in all 275 cases there was a "moment of victory" IYSWIM where the PPC were thrashed in court or discontinued a claim or were called off by a supermarket chain, etc., etc. There will have been at least that number again where they were told to Foxtrot Oscar and then crawled back under their stone. They are eminently beatable but logically when you're in legal dispute you have to put some graft in to beat the other party.