Ask HN: What are the best tips to teach programming to kids?

I find the hardest things for new programmers to understand are variable scope, and execution order.

One of the things I focus on when teaching is evaluating different example code snippets manually, as a "human computer" to double check that their mental model of the interpreter/compiler is correct. Understanding why a variable is shared with a child scope, but not necessarily with a parent in different circumstances is not intuitive, and takes some practice even for intermediate-level programmers.

Here's an example:

Code snippet:

  int result = addNumbers(1, 3)  
  int final_result = addNumbers(result, addNumbers(4, 5))

To evaluate it, these are the steps the computer takes:

  1. int result = addNumbers(1, 3)  
  2. int result = 4  
  3. int final_result = addNumbers(result, addNumbers(4, 5))  
  4. int final_result = addNumbers(4, addNumbers(4, 5))  
  5. int final_result = addNumbers(4, 9)  
  6. int final_result = 13

Teach concepts before code.

For example, if I'm teaching kids what variables are I bring out a bunch of boxes with labels on them. The boxes represent the computer memory. I can put numbers in the boxes. I can put other things in boxes, strings and so on.

I find a lot of people get confused by the difference between a variable name and its value. This isn't helped by the the fact that almost all programming languages use equals for assignment.

Only after showing them the concept thoroughly do I introduce code. I treat code as "telling the computer what I want to do" and the activity as "what I want to do".

Build a game or something he/she likes together, that's what I'm doing, and very smoothly.

Thanks all for inputs.