One spelling, two sounds
SC sounds different depending on the letter that follows, exactly like a single C: before e/i it is soft, before a/o/u it stays hard.
SC before e/i = soft “sh”
Before e and i, SC is one single sound, the sh of shoe. There is no separate k.
pesce
[PEH-sheh]
fish
scena
[SHEH-na]
scene, stage
uscire
[oo-SHEE-reh]
to go out
conoscere
[ko-NOH-sheh-reh]
to know (a person, a place)
SC before a/o/u = hard “sk”
Before a, o, u and before another consonant, S and C are two separate sounds, s + k = sk, as in sky.
scala
[SKAH-la]
staircase, ladder
scuola
[SKWOH-la]
school
sconto
[SKOHN-to]
discount
scrivere
[SKREE-veh-reh]
to write
The H makes it hard: SCHE and SCHI
To get a hard sk before e/i, Italian inserts a silent H, just as in che/chi. The H is never pronounced.
scherzo
[SKEHR-tso]
joke, prank
schiena
[skee-EH-na]
back (of the body)
maschera
[MAH-skeh-ra]
mask
The silent I: SCIA, SCIO, SCIU
If an I stands between SC and a/o/u, the sound stays soft. The I itself is not pronounced: sci + a sounds like sha.
sciarpa
[SHAR-pa]
scarf
prosciutto
[pro-SHOOT-to]
ham
lasciare
[la-SHAH-reh]
to leave, to let go
Putting it together
Il pesce è fresco.
The fish is fresh.
Vado a scuola a piedi.
I walk to school.
Ho una sciarpa rossa.
I have a red scarf.
È solo uno scherzo!
It's just a joke!