Teacher's recommendations:

1. Flamenco West (located in Los Angeles, CA) 

Castanet History

Castanets, also known as clackers or palillos, are a percussion instrument  used in Spanish, Kalo, Moorish,Ottoman, Italian, Sephardic, Swiss, and Portuguese music. Castanets are a member of a very old family of musical instruments that has been found on every civilized continent, with some examples dating back 10,000 years.

The instrument consists of a pair of concave shells joined on one edge by a string. They are held in the hand and used to produce clicks for rhythmic accents or a ripping or rattling sound consisting of a rapid series of clicks. They are traditionally made of hardwood (chestnut; Spanish: castaño), although fibreglass is becoming increasingly popular.

Etymology

The Spanish word for castanets is castañuelas, derived from castaña, meaning "chestnut" or "hazel" -- castanets were traditionally carved from these woods. The Andalusian word for castanets is "palillos."

So What are Castanets, Exactly?

The modern castanet comprises a pair of shell-shaped flattened wooden clackers which are held together with a single loop of string or thin leather. The leather is doubled and the thumb is placed through it, and the pair of castanets then hangs freely from the thumb and is manipulated by the fingers and the palms. Accomplished castanet players can make a variety of noises with the castanets, from a flat "click" to a warm roll. Castanets are always played in pairs, and each pair is tuned differently. The higher-pitched pair (known as "hembra," or "female") is traditionally held in the right hand and the lower-pitched pair (known as "macho," or "male") is traditionally held in the left hand.

Castanets in Folkloric Dancing

Though many people associate the castanets with flamenco, they are not a traditional element of flamenco music or dance; rather, the castanets are an integral part of folkloric Spanish dances, primarily Sevillanas and Escuela Bolera dance.

La Argentina and the Modern Castanet Style

Antonia Mercé y Luque (1890-1936), known as La Argentina, was a classically-trained ballet dancer who decided to leave ballet and explore Spanish traditional dance instead. Essentially reinventing the entire genre, she brought Spanish folkloric dancing to the stage and rebirthed it as a fine art. She was, by all accounts, an astonishing castanet player, and her style of playing became the definitive one. It's no stretch to say that every modern castanet player is basing their style (however many generations removed) on that of La Argentina. 

Castanets in Composed Music

Various baroque and classical composers have used castanets in their scores, though in modern orchestras, castanets that are mounted on a stick are generally used to perform these pieces. Jean-Baptiste Lully used them in many baroque dance pieces, usually to evoke a Spanish or Arabic feel, and they've been used similarly in many other composed works: Georges Bizet's “Carmen,” Strauss's “Salome,” Ravel's “Rhapsodie Espagnole,” Chabrier's “España,” and Massenet's “Le Cid.”

Source: Megan Romer and Mickey De La Serna

Look here: https://flamencokc.wordpress.com/2012/01/20/castanets/

Or here:  https://www.youtube.com/watch?v=QZ6hJ7WkfhE