When my oldest daughter was small, she had a very strong gag reflex (still does, actually). Liquid medicine often made her gag. She just couldn't swallow the stuff, and often ended up vomiting instead -- which made it difficult when it was something she had to have, such as an antibiotic or allergy medicine.
We taught her to swallow pills at a young age with Tic-Tacs. She'd practice swallowing the tic-tacs with a little bit of water by putting the tic-tac on the back of her tongue, taking a sip of water, tilting her head back, and swallowing. If she didn't swallow the tic-tac, it didn't get yucky-tasting on the back of her tongue. It only took a few tries and she had it mastered. Good luck!
**Disclaimer: Read labels carefully. Adhere strictly to dosage guidelines that are appropriate for your child's age and weight. MOST pills that are designed to be swallowed are NOT in dosages appropriate for children. Some prescriptions (like antibiotics) can be dosed for children in a swallow-able pill format. Consult with your doctor or pharmacist to determine the appropriate medicine and dosage for your child.