I remember a heated discussion during the first MOOC between you both (Matt & Tim), I was sparkly new to this world, thus I ducked out of the sparks, but I read the arguments nevertheless.
I have always aligned expectations about formative- type/summative- type assessment with the particular ed sector in hand So, here we go (look out!)
*nursery: baseline them in.....summative assess them out -based on baseline assess (everything in between is formative e.g. pen-portraits/child dev milestones/curriculum expectations)
*Early Years: same
KS1....formal tests year 2 end of year...that is the summing up....everything else formative...
Secondary...well we all know that set up...GCSE / A-level summative....formative can be more than achievement given the project work that was introduced for said quals there and different teachers will have their own skills/technique formative type achievement projects/testing and so on
Uni....modular system so summative is end of module scores....that contribute an overall agg score for degree classification
The above is for England and Wales...because I know these systems
I am not so clear about Scottish Highers and other systems that might vary-will look it up one day-I think it is interesting to consider F/S assess across continents too, especially in consideration of weighting either way.