After discovering my new class had poor investigation skills, I set up an investigation to do every week. You'll need to do your own risk assessment (especially for the slime - I got in a science PGCE student to help!) but mostly is silly fun with science to get them excited and making predictions. There's also an assessment sheet which I gave to all the adult helpers to mark when any child used any of the skills. (I would recommend a ratio of 1:5 for the gathering of evidence and supporting the overall process)