Can I leave Thailand with my ED visa before it expires?

First up, is this a legitimate ED visa, or one of those bogus agency visas?

Talk to your school, inform them so you can get your 90 stamp in advance if necessary. Then you'll need to pay for the re entry stamp at the airport. Don't waste your entire day getting your re entry stamp at immigration.

Any reason why your school can’t answer you question ,,,if they have already what have they said ?

You need to go and get a re-entry permit so that you can come back in on your existing and valid visa.

If you leave without a re-entry stamp you will cancel your existing visa!!!

So YES but get a re-entry stamp first from immigration. (I think it is 1,900 baht)

I highly doubt you're on an ED visa if it's for a year. You're going to be on an extension of stay based on education.

You received this extension because you're taking some type of class and you need to be present in person to attend the class. If this wasn't the case, you wouldn't need the extension.

When you applied for your extension, you signed a document that said you would notify immigration if anything about your situation changes. If you leave the country, you're clearly not attending classes so something must have changed.

Even if you leave the country until your extension ends, you failed to notify immigration that you stopped studying and your situation changed. This is why you will be fined, 500₿ per day from the day you stopped studying up to 20,000₿ maximum fine.

You need to cancel your extension with a letter from your school that says you will finish studying on a certain date and then take that letter and your passport to the immigration office that issued the extension.