I usually say things like 'the expectations are different in year X, so they actually need to do more to gain the same level' I say it with a smile and confidence and as if it explains all. Parents almost always buy it. When they don't I show them an APP type grid and they can often see that their child doesn't actually meet the criteria for the level they though. I don't tell them that at parents evening. Or at least it would be a continuation of previous conversations. There is no way that sort of thing should be news to them at parents evening. If you haven't told them before now, don't do it then. See them after school whenever there is next an incident and say how surprised you are etc. Then keep telling them every single time. Me too! Am thinking I ought to start practising the drinking now!