Quick answer: a prep holds the flyer at shoulder height with the bases' arms bent, while an extension holds the flyer above the bases' fully extended arms - the extension is simply the prep taken to full height.

PrepExtension
Flyer heightShoulder levelAbove the bases' heads, arms extended
Base arm positionBent, at shoulder heightFully extended overhead
Typical useEntry-level stunt, transition pointHigher stunt, often a base for further positions
Typical introductionLevel 1 upwardLevel 1–2 upward, depending on governing body

The Core Difference

Both are foundational two-leg stunt positions, differing mainly in height and arm extension. A prep sits at shoulder level; an extension sits well above the bases' heads, with their arms fully straight.

Why the Progression Matters

Extensions demand more strength and stability from the bases, and more core control from the flyer, than preps - which is why preps are typically introduced first, with extensions following once a team is consistent at the lower height.

How They're Used Differently

Preps are often used as a transition point - many stunts load into a prep before continuing further. Extensions are more commonly used as a stand-alone stunt or as the launching point for single-leg positions like a liberty.

Related Skills

See Liberty for a common next step built from either position, and Half-Up for a position lower than a prep.