"Planning for progression is an important aspect of any curriculum development. Effective planning involves carefully and deliberately sequencing the curriculum content and experiences that teachers ... intend learners to have. These plans should build on previous learning and achievements to promote future learning." From http://waes-elearn.waes.ac.uk/moodle-resources/Basic%20Skills/Pre-entry%20%28D%29/planning/index.htm
During the last few weeks I have had to think about these points a lot. Firstly I have had to write a year 6 scheme up to Christmas with nothing but the word "underground" as a stimulus. And now I am back I am teaching the dreadful OCR Gateway chemistry specification that doesn't allow any progression through it in terms of difficulty - in fact I would suggest it gets easier.
The long term plan introduces the core concepts and ideas that students need to base their knowledge of the next set of concepts and ideas on. The methods and abstract models that are introduced early in the scheme allow students to access the ideas later and the complexity and difficulty of the topics being covered increases through the curriculum.
It might be that this plan is across key stages; what concepts have to be grasped at key stage 3 in order to support progression to key stage 4. It may be within a key stage, for example teaching particles in year 7 means that students can grasp ideas in the atoms and elements and sound modules in year 8.
However, there is also planning for progression in the short-term. For example in a single lesson. The 5E method of lesson planning allows this, by eliciting the ideas students will need, allowing them to use these to explore something else and then using what they have found out to make connects to something further shows short-term progression.
In the medium term a module might allow progression of ideas. For example in acids and alkalis, the progression is from "there are such things as acids" to "there are such things as acids and their opposites alkalis" and move on to "acids and alkalis have different strengths you can measure using pH", to "acids and alkalis can cancel each other out".
SOLO taxonomy is a useful guide to working out if the tasks being asked of pupils are more difficult than the ones before. Or using national curriculum levels, as looking at the way topics have been arranged by their QCA unit there is clear progression in difficulty from year 7 to 9, and it is increasingly possible to access higher levels in the majority of lessons in year 9.
I hate the new GCSE courses and in a lot of ways I believe that this is because they reduce the opportunity for me to do any "planning for progression" in the medium term. I hope that the new curriculum will brig this back. Although I do not expect my wishes to be heard.