Lindseys comments are spot on.
The university I've been associated with for 20 years is quite literally within a mile of the stateline between two states. We draw students from both states and we place students in agencies in both states.
Fortunately both states have licensure (BSW, MSW, & Clinical) and some measure of title protection. We do ask for resumes but a copy of the field instructors state license should suffice to assure their basic qualification.
Then, each year in the early fall, we have an orientation session that includes students entering field AND their field instructor where we do a session specifically addressing details related to Field instruction and the NASW Code of Ethics. Thus students and faculty BOTH have heard our expectations. This session also provides the FI's 90 minutes of ethics training towards their license renewal. (Both states also allow CEU's for -not so simply- serving as field instructors.)
My sense as a former "CSWE reaccreditation site visitor" is that your reliance upon either a resume or confirmation of licensure, would meet the obligation of your "due diligence."
One further note: I just visited with a MSW student in a CSWE accredited online MSW program. At her distant location she was on her own to find and arrange her field placement. The universities guidance (in writing) was that the FI must have graduated "from an accredited program" and hold a license in the state where they practice. The students field instructor is licensed as a "Marriage and Family Therapist" and did in fact graduate from an accredited program. BUT NOT A CSWE ACCREDITED PROGRAM. Such details are important.
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Gary Bachman
Emeritus Professor
Park University
Overland Park KS
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