The amount of studying is dependent upon the percentage of the information a person retains per repetition. The average person requires 8-10 repetitions to remember 90% of the information for most subjects. Some only require 1-2 repetitions (rare). Some people require 30+ repetitions. These repetition amounts are not always uniform across different types of learning. So the same person can require 20 repetitions to learn a new word, but understand a math concept in a single pass.

Why this matters:

Well designed educational curriculum starts out with 8-12 repetitions built in. Then gradually shifts to less in-class repetitions with an expectation for the student to complete repetitions on their own (studying or homework) aka study skills.

For people with a higher level repetition requirement, learning study skills early on in the process is required for success. They often get very early intervention to help them acquire these skills.

For the average student, they are usually taught study skills in a gradual manner as the repetitions in class are reduced. This is part of the curriculum and "homework" design.

For people with a lower number of repetitions, they often don't learn any study skills at all until college/university level. This is when the student is expected to do all of the repetitions after less than a single pass of instruction in class. These students usually breeze by classwork with "no studying" at lower levels only struggle when they eventually need to learn how to study.