The letter S the sound of /s/ makes when you see snakes. Hear the sound of /z/ when your nose smells a rose. Letter s is one of the consonants that vary.
s = /s/ at the beginning of words: sand, sell, sip, soft, sun. It is also the sound of /s/ in beginning s blends: scuff, smell, sniff, spill, stop, swim.
s at the end of words can be either /s/ or /z/: cats /s/ and dogs /z/ need baths /s/ with suds /z/. Understanding voiced or unvoiced consonants can help when s comes after a consonant. Consonants that are voiced make a vibration in the throat which can be felt. Consonants that are unvoiced are quieter and no vibration is felt.
After letters made with a hiss or puff of air, the soft sound of /s/ is often there. In these examples s follows unvoiced consonants f, t, k, p, and th: puffs, cups, cats, sacks, paths.
After letters that make the throat buzz, the sound of /z/ is often what s does. In these examples s follows voiced consonants b, d, g, v, l, m, n, r: jobs, nods, dogs, stoves, files, rooms, pens, stars.
After vowels, sometimes s = /s/
The -ss ending flossy words above have the sound of /s/.
More words with the /s/ sound after a vowel: Fill this bus with gas.
After vowels, sometimes s = /z/
Here are some words where s = /z/ after a vowel: It is easy for boys to choose toys.
When a plural -es is added to words that end with -sh, -ch, /s/, -x, /z/, and /j/, the sound is /iz/ like in dishes, matches, classes, faces, horses, boxes, buzzes and judges.
When you sure like sugar and tissue, you hear that s can also = /sh/.
WATCH the Phonics Focus video on the sounds of s at Youtube. (5:04)
Letter S is covered in Consonants that vary (IV.c) in the Phonics Pow Toolkit with a worksheet and gameboard. Learn how to get a free set of word sort games that includes the two sounds of s. A free word sort game for the letter S is available at the Super Tutor Tools store at Teachers Pay Teachers.