Grammar and punctuation suggestions

[Grammar learner]

Over the past several decades, researchers have described a variety models to describe the instructional quality or the factors that determine school learning.

Caroll (1963), who defined school learning as a function of time spent divided by the time needed.
OR
Caroll (1963) proposed the first such model and described school learning as a function of time spent divided by the time needed.

 

[teechar]

Hello there, and welcome.

Over the past several decades, researchers have [STRIKE]described[/STRIKE] developed a variety of models to describe the instructional quality or the factors that determine school learning.

See corrections.
Remove "who" from the second sentence.
I'm not sure what the second and third sentences mean.

 

[Rover_KE]

I'm still looking for a question.