Tbh bjk, there's not much point going back and tracking his levels over time using data collected by a mainstream primary school. The only consistent thing about this data is that it will be bollocks. The only worthwhile data on levels and progress I have ever seen for my kids has come from independent sources, repeated over time.
Why does it happen? It's basically like Agnes said, but here's the longer version....
To save themselves the hard work of finding out how a school and its pupils tick, Ofsted - and therefore, senior school management - rely on NC level data tracked over time to work out how well the kids (and by extension, the teachers) are doing. Otherwise, they'd have to spend ages in classrooms properly investigating, and we can't have that, can we?
Ofsted want to see evidence of progress. Relentless, metronomic progress, every lesson, every week, every month, every term. There is no space in their approach for the individual child, especially not one with SN. Ofsted deals in dessicated learning units - not human beings, and the levels data means (almost) everything. This is why so many 'outstanding' schools are hostile to kids with SN - their spikiness fucks up the progress tracking spreadsheet, and makes Ofsted unhappy - and we can't have that, can we?
The main problem with this approach is that it places massive pressure on primary schools to show evidence of progress. Unfortunately, small human beings get in the way of this, as they don't always progress in the same way at the same time. If needs aren't being met - as is all too often the case for kids with SN - their progress will look bad. Which will make the data look bad. Which will make Ofsted unhappy. And we can't have that, can we?
So mainstream primaries make a choice. They can choose to measure and record evidence of progress accurately and objectively - and get their arses kicked when the data doesn't please Ofsted. Or they can take a more creative approach to measuring progress - cherry-picking assessments, inflating test scores, or simply making them up.
Very, very many primaries choose the latter - because the chances of getting caught are slim, and much slimmer than the chances of getting a bad Ofsted report if you're honest about the data. Because everyone's doing it, you're a mug if you take the honest approach - and every head knows this. And the schools start doing this pretty much from early years, all the way through to Year 6.
Essentially, it's the same dynamic that saw the Soviet Union report new heights of tractor production each year whilst their factories rusted away - and the same dynamic that sees people die in hospitals so that specific A&E metrics line up. Demented, slavish worship of targets that aren't tethered to reality.
My DS1 left Year 6 with a Level 4 in literacy - age-appropriate. Four independent professionals separately assessed him at the age of 11 as having a reading age of 6.5 and the grammatical ability of a pre-schooler. The levels system is corrupt to the core. Utterly, utterly corrupt.
This corruption affects NT kids too - just ask any Year 7 secondary school teacher about the value of primary school assessment. But the impact of this corruption on kids with SN is far worse. The inflated levels and rates of progress give LAs powerful evidence that mainstream placements are appropriate when they are not. The smoothed-out progress profiles prevent professionals from working out whether specific outcomes are effective. And parents end up being deceived right up until secondary, when the truth tends to emerge.
Sorry, this was far too long, but it's something I feel really strongly about...