If you want to introduce CP exercises to your students slightly more difficult than basic sudoku, you can try this variant: wormsudoku (It comes from the book Taking Sudoku Seriously).
Fill in the grid so that every row, column, and block contains 1-9 exactly once. In addition, each worm must contain entries that increase from tail to head. For blue worms you must figure out yourself which end is the head.
Now I have a motivation to implement Alldiff with precedence ;-) :
Although, the alldiff with preds can only be used for horizontal/vertical/inside a block worms.