The whole, marking and lesson plan things always seems to me to be something which is over exagerated to no end in my opinion, as is the "they go into school during the summer holidays every single day you know" (now unless my teachers had mastered teleportation, or had tunnelled in, there was barely ever a car at any of my schools over the summer holidays).
The last few years at my comprehensive school, the majority of lessons were worked from structured books, set by edexcel or whoever, and published by a publishing company, so where's the planning in that exactly? And unless they reanimate the remains of Mr. Pythagoras anytime soon, is GCSE level mathematics going to be revolutionised anytime soon, or will it still be teaching decimals, ratios, and basic algebra? So once you have it sorted, how is it hard exactly to rinse, and repeat when your current year 10 class goes on to year 11, and you have a new year 10 class? Obviously you have to account for the minor alterations the governing boards change every year, but I've never heard of that drastic a change taking place.