Almost all of the material for introductory Functional Programming requires some knowledge/experiences in imperative programming (like in C, Python, etc). But what I see, Functional Programming is the direct continuation of high school mathematics. Therefore trying to enlighten this link. In the sea of courses like "Functional Programming 101", this material would be "Programming 101 -- in Functional Style".
I hope this would be an option in the early phases of those who are going to end up choosing the Functional Programming Paradigm as their daily dose.
As the name suggests, this will help to build programs using functions as bricks. Therefore, a programming language equipped with function declarations and evaluations would be our starting point. This material will follow a similar approach as Lambda Calculus to express Computations in computers. However, this material does not assume readers to be familiar with Lambda Calculus as this will try to explain them both, treating them equivalent.
This will make use of Common Lisp to practice our knowledge on computers, as it is the closest to Lambda Calculus. Feel free to install any Common Lisp compiler. I am using SBCL. Or, just dive into CondingGround's online lisp compiler to practice on your own.