Quick answer: the first women's cheer skirts were ankle-length wool skirts, part of the everyday college fashion of the time. Skirts stayed below the knee into the 1950s, then shortened quickly in the 1960s into the knee-length pleated cotton skirt - a style popularised by the uniform maker Jean Lee Originals - before shortening further into today's stretch competition skirts.
Early Skirts
When women began cheering in the 1920s and 1930s, they wore the conservative fashion of the day: long, heavy wool skirts, often ankle-length, worn with a lettered sweater. Some religious schools used plaid skirts. These skirts weren't designed for movement - but early cheer didn't involve much jumping, tumbling or stunting either.
The Shift to the Pleated Skirt
Skirts were still below the knee in the 1950s. During the 1960s, as cheer became more athletic, the long wool skirt was replaced by a knee-length, pleated cotton skirt. Pleats let the skirt open and flare during jumps and kicks while hanging neatly at rest - which is why the pleated skirt became the classic cheer look.
Jean Lee Originals, a uniform company from Goshen, Indiana, became the first to market cheer uniforms widely in the 1960s and 1970s, and its owner, Jean Marie Harter, is credited with designing the pleated skirt and double-stripe sweater styles that are still recognisable today.
Changes didn't happen everywhere at once. At Ohio State, for example, skirts were shortened to roughly their current length in 1968 - and the university received letters from people worried about "proper feminine attire."
Shorter and More Athletic
From the 1970s onward, skirts kept getting shorter and lighter, made from synthetic fabrics instead of wool. By the mid-1980s to mid-1990s, mid-thigh skirts with coloured stripes at the hem were common, sometimes with bike shorts underneath.
The Competition Era
Competitive and All Star skirts are now made from stretch polyester-spandex, often in metallic fabrics, and designed to stay in place through stunts, tosses and tumbling. They're always worn with matching briefs. Competition rules set minimum standards - under USASF All Star rules, for example, a skirt must fully cover the hips and fall at least an inch below the briefs. Male athletes usually wear trousers or shorts, and some teams choose shorts instead of skirts.
A Lasting Symbol
Despite more than a century of change, the pleated skirt remains one of cheerleading's most recognisable visual symbols - the shape most people still picture when they think of a cheerleader.
A Note on Dates
Exact dates for style changes varied between schools and regions; the examples above show when changes happened at particular places. The sources we used are listed below.
Sources: Cheerleading uniform (Wikipedia); Of Pompons and Human Pyramids (Ohio State University Libraries)