For KS3, take them very slowly and control the set up process as much as possible. E.g. show or two items of equipment under a visualiser and ask one in a practical pair to collect them. Then do the same again with the other etc. the. Talk through the practical using the visualiser etc

Do you have any tips for making sure students can see the right bits under the visualiser. I struggle to get everything shown, or out of focus. Do you use templates, or something else?