Let's see how much you remember, and then we can start looking.

Back when I was in 4th grade

So this would be, at a guess, 11 years ago?

we had groups of various stories which came in a box set. The sets of short stories (around 30 per set)

Let's try to expand that description a little bit. Were the books paperback or hardcover? (If they were boxed, probably paperback, but you never know.) If paperback, do you remember if they were stapled in the center or bound with glue, like a standard paperback? (This will help to determine the size of the books.) Do you remember if they were more square or more rectangular? Did I understand you correctly, that there was only one story per book?

were organized into different genres, such as Westerns, Science Fiction, Mysteries, etc. We would have to read each one and then answer questions at the end for an assignment.

Were these books used only in school, or did you get to take them home? Were they ever made available to buy, that you remember? Were the questions objective (fill in the blank, matching, multiple choice) or were they short essays? Did they come in colors that indicated different reading levels, and if so, were you expected to read the colors in a particular order?

Do you have any idea what the name of this series was, and if so, know if they're still available?

The short answer to the first question is, no, not yet. :) It sounds like a set of reading curricular units, though, and might have been produced by Macmillan, McGraw-Hill, or some of the other big school text publishers specifically for classroom use.

The short answer to the second question is, maybe, but probably not in the format you remember. Unfortunately, children's books go in and out of print very rapidly. This is less true of textbooks, but those tend to go on a five- to ten-year cycle, after which things get changed around to reflect the latest research and newest fads in education (former: good; latter: silly). The good news is, many adults are now interested in the instructional materials that were used when they were children, creating a kind of nostalgia market. The Dick and Jane books are making a big comeback now. (God knows why. I thought they were really stupid when I was little.) So someone could have gotten hold of the collection you remember with such fondness and reissued it in another format.

What state was your family living in when you were in the 4th grade, and did you go to public school there? If it was a curricular item supplied or provided through the State Dept. of Ed., some record may exist at that level. Or a teacher may remember. They are often very cooperative about their past careers. If it was a private school, we will have to enquire there, specifically. They often buy their own materials, though sometimes they also go through the state, and if they are religious schools, they also buy from catalogs of approved materials which may not have overt religious themes.

I still remember some of the science fiction stories and would love to add them to my collection.

If you remember any of the plots, titles or authors, a separate search can be launched from that direction.

I bet they're out there. Probably used, or maybe collectible in other forms. Maybe an original is even in a university library with a strong education program. They tend to collect curricular materials.

If any of the information about your early education is too specific for you to be comfortable posting it here in public, we can get to those items through Robert, once he gets back. I seem to recall that he'll be "out of the office" until after Memorial Day. That supposes, of course, that you want me to pursue this in greater detail.

Let's see what we can do.