These worksheets are to help students distinguish between the unvoiced 's' and voiced 'z' sound. Practise the pronunciation of each pair of words with the class, highlighting the difference between the sss and zzz sound in each pair of words. Then give them the picture sheet and students match the pictures to the right pairs of words. I used lots of example sentences to clarify the meaning and also show the correct pronunciation, I think it worked pretty well. Hope you find this useful.