1970s Greek Mythology schoolbooks with kids who “discover” mythology

Question

I am trying to recall the name of some educational workbooks and characters that would have been in circulation when I was in 3rd grade (United States around 1974).

These texts were part of the curriculum at the public school I attended and were used to teach Greek Mythology. My recollection was that the books were centered around a couple of fictional kids who "discover" mythology or are led to it by uncovering secrets about it through "teenage sleuth" type adventures. I can't recall for certain, but it seems like there may have been some kind of portal that allowed the kids to actually enter the Greek Mythology realm.

I recall the books had quite a few illustrations as you might expect in a grade school educational books. The books were used as a vehicle to generate interest in mythology.

Answer 1

I think this is what you're looking for.

Sullivan Programmed Readers, McGraw-Hill publishers, Cynthia Buchanan

BTW, the "these" link in the comments in the link above doesn't work. It goes to an eBay auction for an item that was taken down.

And a list of libraries in the US that actually have copies.

Okay, found this one on Amazon. Book 20 of the series.