This isn't evidence you are a bad teacher and no sensible HT would look at spelling scores in isolation and think so. But you may well have to give some ideas as to what you are going to do about it. If asked about it (if no one asks then don't make a song and dance about it!) then you could say that you have been concentrating on the LA children and have possibly done this too much. Then set out how you will address the balance and ensure you HA make progress in this last term. If it was me I'd not get the children to resit the test, what would be the point? I would just shrug and move on, SWST isn't a definitive guide to attainment. I definitely wouldn't be initiating discussions, though if they asked me I'd have a plan ready to tell them. I'd be thinking what to do about it and ensure all children make good progress before July when I'd do their final SWST.