"Residential Treatment Center (RTC)" covers a range of places, so the first step is identifying the issues (and their depth/extent) calling for such a placement. Most RTCs I know about deal with behavior-related issues, and often drug abuse as well. Some are a small step from being a psychiatric hospital., and others may look like "just" a boarding school. If the issues have a physical cause/base vs. "only" acquired behavioral troubles, that calls for a very different assessment and treatment focus. And, whether or not they are called an Residential Treatment Center (RTC) may depend on state law or on marketing (including funding) considerations. Effectiveness depends a lot on getting a good match between facility and needs.
Academics vary also, but most will provide what I'd call just adequate education. State laws generally require education, but the focus is properly on addressing the issues that led to the student's placement.
There is an Residential Treatment Center (RTC) in Pennsylvania that I'd describe as a "tough" place, and they deal with some very difficult behaviors. They sometimes get some unfortunate publicity, but remain one of the best around for what they achieve. You need to dig a little. And, you need to understand why any place does what it does, including any restrictions on communication. (There are some excellent reasons for limiting communication, and there are some not-so-good ones as well -- more reasons to dig a little.) It is possible to find something negative about most places, and much much harder to find independent good reports.
If your son has been getting for many months all that is available while he still lives at home and there is no real improvement, and any diagnosis seems right, I'd lean toward a long-term placement. That could be anywhere from 9 months and up for a place with a standard basic "program". If he is already getting services from (funded by) his local schools, this would just be another step, and may well prove cheaper for them over time, especially as it should prove effective.