It was around 1959-60 and everyone in the 1st grade was given a Sheaffer cartridge fountain pen to learn to write (plastic school version in red, green, blue and clear bodies). Those early cartridge versions made it much easier for the students and the teachers, since the inkwells were not necessary anymore. A couple of years ago, I purchased one of those NOS pens for old times sake (and re-live my childhood), and fell down the rabbit hole hobby of modern fountain pens!
I know the model of Sheaffer cartridge pen that you were using very well indeed. In the early 2000s I used to buy job lots of pens from ebay, sometimes 40 at a time and the Sheaffer Cartridge pen was a frequent purchase. In addition to being a school pen they were often overprinted with the name of a business, especially auto dealers or boatyards, I can imagine that they were giveaways to customers. a good idea, keeps the name of the business on the desk and front of mind for every customer
You might also remember this magazine ad which included the yellow end cartridge, the idea being that there was a right and a wrong way to insert the cartridge, you inserted the cartridge into the barrel, the cartridge was pierced when the barrel was screwed down onto the section.