Checkout the CET STEM Lending Library (new STEM resource being added all the time)
A range of activities that you could use with a class or extra curricular STEM group. Split into Primary and Secondary, these are thorough and well resourced activities
(predominately primary based at present)
is a free 4-lesson classroom resource - contains 45-60 min lesson plans designed to engage students in Engineering (aimed at Year 7-10) .