For an educational website, a .org may be best. It lends itself credibility in the mind of your viewers, and it's not much harder to rank a .org from a general standpoint - I'm not sure if any added difficulty is lessened given that it's educational, and thus it may even be easier or at least not a disadvantage to have a .org (just theoretical).
For example, do searches for various educational keywords. You'll find that many of them - if not all of them depending on the keyword - are .orgs.
What generally makes extensions besides .com difficult is that you're often pitting a .net/.org/.info against several .coms. So it could be 1 .net vs 100 .coms. Naturally, the .coms have the advantage, which makes ranking another extension difficult and why it's usually advisable to have a .com.
However, when you get into educational keywords, your competition is different. It could be like 1 .org vs .60 .orgs and 1 .org vs 40 .coms. Theoretically, this lessens the usually difficulty you would have ranking a website that isn't a .com because all the other​ websites also predominantly share your same extension, and so your .org is no longer an outlier like it would be if you were facing 100 .coms.
That said, it's not advisable to purchase the .org version of a website if the .com is taken. Find a name that is unique to you and isn't taken in some form or another.
