Hi Willa Gayle,

To take the SCAT, you need to first register with the talent search (jhu cty). http://www.cty.jhu.edu/ts/acceptabletests.html
Look it up you'll be able to do an application (with standardized test results over 95% or teacher's or parent's recommendation). You'll have to pay a fee. They'll give your son a testing number (ours was sent by mail a few days later) and then you find the Prometric testing center closest to you http://securereg3.prometric.com/ProfessionalHome.aspx
They are good about having weekend testing times. They have a fee, too. If you're not going to use Johns Hopkins programs but are interested in closer programs (Northwestern U.), first check which tests they require (I think everyone else uses the EXPLORE). Cym