There are positions called "Therapeutic Support Service (TSS)" that generally only require a bachelor's degree in psychology. Such support personnel may receive training from their employers to qualify for a behavioral therapy credential.
Credentialing for mental health services are regulated at the state level, despite the fact that many credentialing examinations are national. So, depending upon the state in which you wish to live and work, you need to find out as much as you can about the regulations that govern practitioners. Many behavioral therapists have a master's degree in psychology and/or the LPC credential (licensed professional counselor). I know there are certifications for behavioral therapists....but I am not as familiar with such credentialing as with that for the LPC.
I suggest that you check out the website of the American Counseling Association (www.aca.org) for more information, in general, and the LPC credential in particular.
You might want to check out school psychology master's level programs if your desire is to work with children in school settings!
Linda Ann recommends the following next steps:
A minimum of a master's degree and state licence is required of all therapists, but many behavior therapists hold doctoral degrees. Education begins with a bachelor's degree in psychology and continues with graduate programs in psychology or counseling.