The main issue is that pupils are going to appear to have gone backwards. Schools continuing with a levels-based system are planning to assign those pupils that have met all the key learning objectives for that point in the year a sublevel/point score that historically indicated age-related expectations (ARE) under the old system. So, a pupil that has met all learning objectives for the end of Y4 will be assigned a 3b/21 points, because that's how it used to work. That's the theoretical equivalent.
Sounds fair enough.
However, the new curriculum does not translate into levels, and those old 'age-related expectations' are not a proxy for having met the key learning objectives of the new curriculum. Implying that they do is going to cause problems. I'll give you an example:
A pupil finishes KS1 with a L3 in reading (that's around 30% of pupils nationally last year). And as you may or may not know, a L3 is treated by the DfE as a secure level 3, i.e. a 3B (21 points). Now, under the old system of levels, a 3B was considered to be age-related expectations for the end of Y4. In the new curriculum, a pupil deemed to be at age-related expectations at the end of Y4 will have met all the learning objectives for that point in the curriculum. So, ask yourself this: has the KS1 L3 pupil done this? The answer is almost certainly no, which means you can't really continue to assign them a 3B. Instead they will have to be assigned a new sublevel; a translated value that reflects their position in the new curriculum, i.e. above expectations, but not 2 years above. Maybe a 2A. Who knows?
In other words, they've apparently gone backwards.
Which is daft.
Some tracking systems have not helped matters by a) allowing users to continue with levels, and b) mapping new values back to old point scores and sublevels, implying there is a simple conversion.
I suggest schools do themselves a favour: ditch levels now. You'll have to at some point anyway. Adopt a new assessment system and avoid the pitfalls that will inevitably arise by giving the impression of data continuity. A new system will not invite such comparison. You can start afresh.
So, use your historical data to show progress and attainment up to the end of last year, and then start again this year. Don't attempt to measure progress across the old/new NC boundary by using end of last year assessments as a baseline. Instead create an early autumn assessment and measure progress from there. Concentrate on tracking percentages of pupils that are below, at and above ARE; hopefully showing increases in those at and above ARE as the year goes on. Individual progress comes down to books and the percentage of objectives met. That's pretty much all we can do at this point. Next year things get easier because you'll have a compatible baseline for more in depth and reliable analyses, but producing the 3 year progress data stipulated in the Ofsted guidance is not going to be easy. I just can't see how it can be done with any degree of reliability and I'm not sure they've thought it through. I suspect these issues will become increasingly apparent over the course of this year.
And finally, I know that many tracking systems are not quite up to speed, and Ofsted make provision for this in the new guidance (see Ofsted handbook p63, para. 191). So, I'm not advocating throwing everything out but do make sure you ask the right questions of your supplier. It's fine to hold on (for a bit) whilst new versions are rolled out but make sure they have solid plans for assessment without levels (hint: they should have already!). It must be very tempting for established systems to stick as closely as possible to levels and APS because it requires a lot less redevelopment. But that doesn't necessarily mean it's right for schools.
Remember: the tracking should fit the curriculum, not the other way round.