Schooling
Process of familiarizing a horse with the starting gate and teaching it racing practices. A horse may also be schooled in the paddock.  

Scratch
To be taken out of a race before it starts. Trainers usually scratch horses due to adverse track conditions or a horse's adverse health. A veterinarian can scratch a horse at any time.  

Shadow Roll
A (usually sheepskin) roll that is secured over the bridge of a horse's nose to keep it from seeing shadows on the track and shying away from or jumping them.  

Shank
Rope or strap attached to a halter or bridle by which a horse is led.  

Shedrow
Stable area. A row of barns.  

Sheets
A handicapping tool assigning a numerical value to each race run by a horse to enable different horses running at different racetracks to be objectively compared.  

Short
A horse in need of more work or racing to reach winning form.  

Show
Third position at the finish.  

Show Bet
Wager on a horse to finish in the money; third or better.  

Shut Off
Unable to improve position due to being surrounded by other horses.