I have chosen option 1,
With a premade data set, that has missing cells etc,
step through the processes 1 by one with the students or teachers, allowing them to do it at the same time and ask questions as they do it.
1. load data
2. visually check data – are there missing cells? obvious errors?
3. discuss options – it that data necessary? can it be fixed?
4. clean data
5. check data is still functional and in correct locations
then allow a new, but similar data set to be loaded for assessment and students/teachers complete on their own and hand in for checking.