I've tutored a number of introductory CS students and have found w3schools.com to be a fantastic source of reference material for students. Years ago there was some controversy with the site because it taught web standards / conventions which deviated (slightly) from the consensus of sites like stackoverflow. Since then they've made a number of corrections and for the most part have really great content.

Here [1] is a good discussion on quora on the topic. You'll notice that the main complain is out-dated information when compared to MDN. I would argue that MDN is a much deeper source of information that can overwhelm beginners when all they need to know is say, what a <p> tag is.

Please please please qualify these kinds of statements when giving information to beginners who can be easily swayed in the wrong direction by well-meaning individuals such as yourself.

[1]:https://www.quora.com/Does-W3Schools-really-suck