Can an ED Visa in Thailand cause issues for future visa applications or entries?

My friend had a serious talking to when we came back from VN. He was on an ED visa for a few months. IO asked him to speak the alphabet and asked him questions in Thai. That didn't go so well. So off to the little room in back. After his Thai gf talked to the IO, they let him but made a notation about his visa. His 50th BD was in a week and we went for a retirement visa.

So it seems your actually have to be a decent student to maintain the ED visa

As far as immigration concerned, there are only 2 kinds of ED visas.

1) Formal education, for university students seeking a degree. These are an initial 90-day visa followed by annual extensions until you complete your studies.

2) Informal education, for language and muay thai students. These are an initial 90-day visa, followed by up 3 more 90-day extensions, totaling a year.

Whether your school is reputable or not, makes no difference to immigration. They don't know what you school you went to and don't care, they just know if you had an ED based on formal education or information education. If your record shows a history of an informal education ED, you are likely to have problems for multiple years after you have this visa. That is because it's the most abused visa type, which replaced the volunteer visa many years ago after they basically stopped issuing that visa.

During the 1-year stay of study, you should NEVER leave Thailand. Countless reports of people immediately denied entry upon returning, because they told immigration they needed a visa to study in Thailand, that studying in Thailand was so important to them they needed a visa for it, and then they left Thailand. Doesn't matter if it's for the weekend, over a holiday, or what. You are almost guaranteed to be pulled out of line and interrogated, and very likely to be denied entry. There are reports of people who have letters from school giving them permission to leave, including all relevant information on dates, etc. Immigration officers even call school official and speak to them, and still deny entry.

Once your education extensions end, you are still likely to face scrutiny if you try to return to Thailand as a tourist for multiple years after this. They see you lived in Thailand, and don't want you returning again as a tourist, as they expect you are trying to either continue living in Thailand, or trying to live in Thailand again, which you cannot do as a tourist.

You should not have any issues in getting other visas even if you have ED in your past, and you should have no issued entering on any other visa type besides tourist entries after that.