Can I obtain a student visa stamp after a one-day trip to Laos while on a visitor visa in Chiang Mai?

What is visitor visa? I never heard about that.. Visa on Arrival, visa exempt or TR visa... No you can't... ED visa not just a stamp.. first you need a contract with your school.. they need an approval letter from The Ministry of Education.That process itself can take 3-4 weeks. After the school or agent (if you using an agent for the process and not the school doing for the whole process for you) will submit the paperwork to the immigration office. And you need a place where you can stay long term because you need TM30, lease agreement... So definitely not a one day process and just a simple stamp in your passport...

Next time do some research... Some school can do for you a visa conversion when you are in the country but still takes time... I don't know how long you are here already...