These are the variables the students came up with after making the models :)

As you can see there's so many more variables now! However, they have yet to consider the 'number of valence electrons' (electrons in the outer layer only) as a variable (because I haven't introduced this term yet) but also they haven't 'spotted' the pattern themselves yet, though you can see the writing in green is me trying to provoke them into looking at it a different way...

They needed to 'build' the periodic table using their models to spot this very important variable. It was hard to get them to USE the models without specifically telling them how to (but I desisted from doing so...).