Road Scholar is the big dog in the educational cruises department. It’s been mentioned in several threads including this one:
I went on two of their excursions: one to the Grand Canyon and one to Alaska. Both had their pluses and minuses.
Pluses: Small groups (< 25 people), some less “touristy” stops, all-inclusive and no tipping (I even opted to get airfare included), very knowledgeable guides and programs. Lots of choices for unusual tours (e.g., to check out the polar bears in Canada).
Minuses: There were no travelers under 50 on the tours – and those in their 50s and 60s were with older relatives. RS does offer grandparent/grandchild tours that are more younger person friendly. This may not be a minus for you. It was kind of depressing being reminded of my demographic for the whole trip, but I was grateful there were no youngsters around too. The accommodations and food were good, but not at all glamourous; if you are looking for the luxury hotel experience, RS is not it. Our tiny ship on the Alaska cruise was old and cramped. The Grand Canyon trip relied on an elderly bus with defective air conditioning (too cold) for our tours. The trips were very expensive up front compared with more commercial tours, but probably break even when you consider that gratuities and excursions are included.
I felt both RS trips were positive experiences but I don’t think I’d go on another one.