FadedC is correct. There are no differences. You can find masters programs that award the degree with 70+ credits, or EDS programs that are closer to 60 credits. And vise-versa. There is no difference. To clarify one misstatement posted previously, any NASP program MUST be at least 60 credits. This is REGARDLESS of the type of degree (i.e. MS, MA, M.ED, ED.S, etc.).
NASP recognizes all sub-doctoral level programs that meets its standards for accreditation as "Specialist-level" and recognizes all doctoral level programs that meet its accreditation standards as "Doctoral". A "specialist" program, according to the NASP accreditation standards, require "The program shall include at least 60 graduate semester hours or the equivalent, at least 54 hours of which are exclusive of credit for the supervised internship experience."
Here is a link to the NASP accreditation requirements
http://www.nasponline.org/standards/finalstandards.pdf
To make matters more confusing, every state has different requirements. Some states require this NASP minimum, some states require fewer credits, and some more. Some states require a "specialist degree" specifically, others require a "masters" degree. When this happens, the applicant must prove "equivalence". Only about 2 dozen states recognize the NASP accreditation. In some ways, getting recognized and certified as a school psychologist in a state can be comparable to licensure as a psychologist (although, overall, I do NOT think it is as difficult).
It is confusing. Some programs only award a masters degree. Some only an EDS. Others award both a masters and an EDS (such as a masters after the first 30 or so credits, and then the EDS after completion of more advanced courses and internship). Still others call the degrees something entirely different (e.g. Certificate of Advanced Graduate Study (CAGS). To further add to the confusion, some programs award a masters of science, a masters of arts, or a masters of education. It would be nice if NASP set some sort of descriptive standard for the degree. They could state something around the effects that any NASP certified program must award a masters degree or must award a masters + EDS degree or something to that sort.
Like FadedC mentioned - look for the NASP accredition if you are going sub-doctoral level for school psych.
As the previous poster said, many specialist degree programs just call themselves MA programs. You can't really go by the name of the degree, that means nothing, which as you say is very confusing. Either way someone should definitely only go for a degree that meets NASP guidelines regardless of whether the degree is called a MA or something different.