If you have not already done it, then the pressure is on to complete your Head's performance management before the end of term. Setting targets is a challenging task for both the reviewers and the Head - for what do we set targets, how tough should they be?
For me this also raises the interesting territory of 'Lead' and 'Lag' indicators - improving teaching and learning (if we can find a way to measure it!) being a Lead indicator that leads to improved outcomes/attainment, a Lag indicator.
Early in ther implementation of targeting sytems we often end up with lag indicators (cohort performance, staff attendance, etc) whereas as they become more sophisticated we can move to the Lead indicators that we believe will eventually produce improved performance. This might be regarded as a shift from management to leadership.
...and how tough? My guidance, and I have facilitated the implementation of PM systems all over the place, has tended to be "deliverable, but only just". They need to be challenging enough for yor Head to have to think differently but not so challenging that they don't even try because they are obviously undeliverable. So improving pupil attendance from 80% to 95% in 1 year is likely to be undelliverable, whereas to 85% could be a real challenge yet achievablke with a following wind.
This in turn leads to consideration of success criteria. If everyone's targets are all delivered, then they were not tough enough. I accept that soemtimes a target might not be delivered; the trick here is to satisfy myself that a serious effort has been made and that unexpected factors intervened to inhibit delivery.
What do you thinnk?