Giving shocks to students
These sorts of experiments are safe so long as the teacher takes care to follow standard guidance such as Van der Graaf Generator Safety which goes into some detail.


  The electrostatic energy stored by the sphere should not exceed 0.5 J.


...


  An enquiry to CLEAPSS has revealed no recorded incident of direct injury caused by shocks from the correct use of school Van de Graaff generators. 


and so on.