airplane kits like the Great Planes PT-40/PT-60, the Goldberg Eagle 2, and the Sig Kadet Senior/MkII/LT-40 continue to sell to modellers around the world. Why? Because they're classics!
I don't view any of these models to be classic designs. Anything built with lite-ply misses the boat on classic by a decade or two.
A short list of classics would include:
Smog Hog, Esquire, Champ, Falcon 56, Skylark, Sr. Falcon, VK Cherokee, Astro Hog, AeroMaster, and Trainermaster. There are many others of that generation, that were all balsa, spruce and birch ply.
I've not owned a Pulse 40 yet, but have flown a couple. Fantastic sport flier, much like many of the classics I mentioned, but structurally as weak as anything else built today from lite ply and air. It would not held up to the rigors of model flight when radios didn't always work.
The School Boy and School Girl were designs by Ken Willard. Ken and I were in the same club in the bay area for a time, and we had several interesting things related to flying. He sure would have enjoyed today's ultra-small radios and electric power systems. He predicted radios would eventually get down to under 2 oz back in 1970 when most light weight systems weighed 9 to 13 oz.
Classics are some what subjective to how far back your experience reaches.