I have discovered that the practical skills of many of our students are not as good as I would like them to be. This has led us to think more carefully about the practical work that we do in KS3 and how we focus on the skills that they need for KS4. This is a work in progress, but we aim to make the focus of the practical more explicit and give them lots of opportunities to develop the skills that they need.
In terms of assessment, I have collated a number of questions about practical work that I use in class with the practical or as part of an end of unit test. The questions have been taken from the IGCSE practical exams and specimen papers. I really like the PRODMEE approach that @teachingofsci has blogged about here and have used something similar with our evaluation cubes. This has been quite a successful way of getting students to really think about the different aspects of the practical work that we have covered.