I think this is quite likely. Browsing Guatemalan school sites it's clear that many of them operate the US grade system, and there are a number of examples of the use of "8th", "10th", "12th", and so on, referring to grades, even in pages that are in Spanish, or partly in Spanish. It's not likely to be an English-style date, because if they did that they would almost certainly follow US practice and put January/Enero 10th instead of 10th January/Enero (putting the day first is typically British, as Noni has said).

Here's an example from someone's page on LinkedIn:

"Profesor Interino - Physical Science, Chemistry and Environmental Science
Colegio Maya de Guatemala
November 2010 – December 2010 (2 months)Guatemala
Profesor interino en Physical Science (9th grade); Chemistry (10th y 11th grade); Environmental Science (12th grade)."
http://www.linkedin.com/in/profedgar

Note "10th y 11th grade": it's in Spanish (well, Spanglish), but he's using the US English terms. In the same way, if we were writing in English about a school using the Spanish grade system, we might say "Fees for 3º ESO", for example, using the Spanish format.

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Note added at 1 hr (2013-01-31 12:07:19 GMT)
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The likelihood that this is correct would increase if you have other evidence from your text that the school in question operates US grades (or if you can look up the name of the school on the Internet and confirm it that way), and also if 10th grade is compatible with the age of the child; children in the 10th grade are normally 15 or 16.