"material" vs. "materials"

Question

From Cambridge Dictionary, Meaning of "lesson" [ C ]

a period of time in which a person is taught about a subject or how to do something

From Cambridge Dictionary, Meaning of "material" [ C or U ]

information used when writing something such as a book, or information produced in various forms to help people or to advertise products

EF is an online English learning platform which sells lessons. An EF lesson consists of some questions, answers and a vocabulary list containing dozens of words or phrases regarding a specific topic and usually lasts on hour.

I guess learning material in this context could refer to a vocabulary list in an EF lesson or the whole lesson in general.

A friend asked me about the platform yesterday, because I had been its paid classes. Here is part of my reply.

Most of the material in the EF lessons are not very practical. What kind of people would use personal checks in daily life?

I used the word "material" as an uncountable noun and "lesson" as countable. Did I use the correct forms?

Should I have used "material" in its plural form?

Most of the materials in the EF lessons are not very practical ...

Answer 1

In this case both are correct. 'Material' can be both countable and uncountable.

If used as uncountable, your are treating the material as a mass. If countable, then you have treated it as divided up... perhaps into different categories: questions, answers, instructions, etc.

Answer 2

Your usage is fine. As @VaugnOhlman says, "material" can be either countable or uncountable. If you use it as uncountable, you are speaking of "material" as a mass. If you use it as countable, then you are speaking of individual units of material.

Many words are like this. Like if I say, "Fire is hot", I am using "fire" as an uncountable noun. That is, I am speaking of the general idea of fire. But if I say, "Both the fires at our campsite are very hot", then I am using fire as a countable noun, and I am speaking of two specific fires.

One quibble with your usage: When you use an uncountable noun, you use the singular form of the verb. "The material is ...", not "The material are ..." "Most" here makes it tricky, but it follows with whether the thing we are taking most of is countable or uncountable. "Most of the material is ...", but "Most of the lessons are ..."

And just by the way, not really related to your question, but the definition you cite for "lesson" is not the correct one for the context. The type of lesson you're talking about is not a "period of time spent learning" but more like "a collection of educational material on a specific subject". I'm frankly surprised that the page you cite does not have such a definition. I looked at https://www.thefreedictionary.com/lesson and their definition 2b is closer to the sense you're using here.