In MA, ridealongs are not necessary to pass an EMT-B course. I have been on ridealongs in the past but none through my EMT-B school. You can just call local ambulance services. Most ambulance companies, especially fire departments will always be excited about your interest and take you in for a day. At the time I had a First Responder cert but I don't think you need anything, ridealongs are almost always going to be completely "Hands-Off".
Around here, when you first get hired for a company, that's when you start doing your observation hours. Depending on the company, you may have to do a certain amount of hours "shadowing" two (or whatever) other EMT's, and then get paired up with a veteran EMT once you start.
Ambulance companies vary widely with their protocols(some have their own tests you have to pass even if you have an updated cert). And I'm sure, paramedic school is totally different, I have looked at some of those programs and most include observation hours/clinical trials as part of training.