What's happening here is that your school is running a firewall / proxy between your school computers and the rest of the Internet. It's only allowing certain web traffic through.
You need to speak to your teacher or directly with the school IT helpdesk and make sure all the following sites are "whitelisted", i.e. are allowed. (This is the official list from the Codecademy Help page : https://help.codecademy.com/hc/en-us/articles/220441848-Why-can-I-not-access-the-Codecademy-Learning-Environment-)