It seems weird to teach kids to use an outdated way of declaring variables. I know that code.org isn’t on ES6 yet, but I feel like that should be a priority. (same issue with default parameters for functions)
if you are aware of how CDO works, you would know that it uses an interpreter to run the code. Meaning that it’s running it’s own custom sand-boxed version of ES5 to migrate to ES6 would be a huge undertaking! Not to mention many of the lessons would have to be changed or redone entirely because of this. Additionally a bunch of personal projects on the site would break due to the changes built on ES5 architecture and possibly some more new ES6 exploits. And as you know CDO is a voluntary organization if you think you are capable of this change feel free to add it yourself on the github which should be under the name of code-dot-org, either that or feel free to ask the support team yourself (although i don’t think they would know)