This article really answers your question, but I'm not sure if you can see it if you're not a member of NASP or if it's behind a pay wall. Basically, in the Northeast, only 32% of specialist-level school psych interns get paid, and the average stipend is $12,764. That's the lowest percentage and amount in any of the four regions. (Doctoral interns have it better, at 67% and $15,740, but are still the lowest among their peers in other regions.) The Northeast just has a tradition of not paying their interns, and since people keep taking the internships, they can keep doing it.