Hi feelingood:
Although I do not commend WellThen for his/her tone - s/he is correct in that what is happening is the new teacher is doing their job - which includes demonstrating progress over the year they teach your child.
This is my theory (and this has caused a storm previously - so I stress many do not agree with this).
It is only a theory - but it seems to be something teachers (on the MN staffroom www.mumsnet.com/Talk/the_staffroom & parents here on MN primary talk are also recognising...
Not sure whether your DS (now Y3) has moved from a different infants school or is in the same primary (combined infants & junior) - but there does appear to be some gaming of NC Levels/ APP points/ progress measures (whatever your area uses).
In schools around here, staff management of efficiency is related to raising all pupils at least 2 NC sub-levels (or equivalent APP points) - so low a behold moving children back slightly does rather make one's job that bit easier.
Does it affect your child. No not really. They may even improve 3 sub-levels but what that does is demonstrate what a fantastic job the teacher is doing - and I suspect when performance related pay comes in this kind of rolling back of achievement against the previous year will become the norm.
As a parent we're piggy in the middle - each year it will be in the teacher's interest to show a certain standard (usually 2 NC sub-levels around here) of progress - and the next year the new teacher can turn the clock back. I've had drops of sub-levels - or with a child who had nearly achieved all ticks against targets on APP style sheet at end of previous year, I was told outright by teacher that the school policy was to start that level again if not completed - so each skill had to be observed by teacher or TA 3 times - again 'loss of learning' over summer was cited as the reason for the school-wide policy.
My view is you can't blame people for ensuring that they meet their work preformance targets - but you need to be hawk-eyed that the notional elements of the national curriculum for that year are covered & mastered by your child.
My reality checks are:
Campaign for Real education has curriculum statements written in plain English for primary school here: www.cre.org.uk/primary_contents.html - this is gold standard but does clarify what is possible to achieve in ideal circumstances. It is likely that your school won't quite be working to this - but it is good to understand what 'gold standard' looks like, rather than take school's endless statements of 'working to the highest possible standards' at face value (we've come to joke about 'possible' in this statement and one school-gate pal adds 'for us' after it).
The draft national curriculum documents (which will be finalised for 2014/ 2015 school year) give a good signal about what should be covered (and therefore mastered) when. Info here: www.education.gov.uk/schools/teachingandlearning/curriculum/nationalcurriculum2014/nationalcurriculum/a00210036/sosletter - just select area of curriculum you are interested in within light blue box on right of webpage - and then search for the year in KS1 or KS2.
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However the wrinkle in all this is that NC Level assessments are going to be abolished and schools can devise their own means of assessing progress - info here: www.education.gov.uk/schools/teachingandlearning/curriculum/nationalcurriculum2014/a00225864/assessing-without-levels.
As a parent - what I think would help is to have something which on the ground seems consistent and reflects reality. I don't think it helps to shelter parents from the news that their DC is struggling. And to be honest, having been their in technicolour with DD1 - it harms the child (as early intervention/ support can make a huge difference with struggles in early reading/ maths).
HTH