Creating a tear-away dance costume is not as complicated as it seems; the simplest solution is to alter an existing costume. By tearing out some key seams with a seam ripper and sewing Velcro into each side, an ordinary dance costume (or other ordinary clothing) becomes a tear-away costume.
Choosing the Costume
If you want a durable costume you can use many times, choose your original material wisely. A slinky, thin fabric such as lamé will look great and tear easily...the first time. It is not a durable material. On the other hand, a durable, shiny fabric like glitter dot holds together surprisingly well, although any sparkly fabric will lose its sparkle after a while. Cotton is durable and with its minimum stretch, easy to convert to a tear-away version. The sturdier the fabric, the more times it can withstand being torn.
Choosing the Seams
Deciding which seams to rip out and replace with Velcro is key to your success. For pants, rip out both outside seams, just down the outside of both legs. Don't rip out the inside seam as well, or you may end up with two halves of pants which are more difficult to tear away.
For a button down shirt, leave the buttons on the front and simply sew little squares of Velcro, so the shirt closes as normal. These kinds of shirts, already built to withstand stress on those areas, work great for converting to durable tear-away costumes. You can also make the arms tear away by ripping the seams out of the shoulders, all the way around the top of the sleeve (not down its length) and sewing Velcro into each side. A skirt requires only to be slit once from waistband to hem, then reattached with Velcro. Tank tops and underwear should be either cut or have the smallest seam ripped, such as the straps to the tank tops or the sides of underwear. The smaller the seam, the easier to tear away.
Choosing the Velcro
You'll want to locate a Velcro that's near the same width as the seam you are tearing out. If you cant find a narrow enough Velcro, bigger Velcro trims down easily with scissors. Don't buy the super strong Velcro, as it will be hard to tear. Also avoid buying the self-adhesive Velcro that only gums up the needle. Velcro comes in mainly black and white, but shop around for the color that will be least conspicuous.
For long seams like pants, you may want some gaps in the Velcro for easier tearing. Small sections (about 2 to 3 inches) spaced 1-inch apart will tear much easier than a solid seam of Velcro. The only downside is the the seam won't look as smooth and it may be apparent that they are tear away.
It is usually efficient to sew around the outside of the Velcro, no need to cover the whole piece with stitching. If you want it to be extra secure, you can sew an "X" from corner to corner as well.