If you are a resident of a MERCOSUR country, then you don’t need a visa to enter Argentina. However, you will require an official letter of enrollment from the recognized school in Argentina. On the other hand, for Non-MERCOSUR residents, a tourist visa and an approval letter from the school is required to enter Argentina.
For students who wish to pursue their studies in Argentina, a specific category of temporary visa is required.
23 J Visa- It is applicable for students who wish to enter the country for secondary, tertiary, university or specialized courses. The students can be from regular public or private colleges that are officially recognized.
The Student Visa once issued is valid for 6 months to one year. The tenure can be extended depending on the jurisdiction of Argentine consular.
Source : http://www.mrecic.gov.ar/asistencia-consular/tr%C3%A1mites-para-extranjeros#01