Your letter is just fine. There are only a very few edits.

Dear Sir or Madam, -- Do you not have the name of the person you should address this to?
I am writing this letter to recommend [NAME] for admission to your Study Abroad Program.

I have known Mr. [NAME] for two years as a student of [PROGRAM] at the University of [CITY], [COUNTRY], and he has always shown a strong interest in our program. Personally, I taught him Project Management and Introduction to ERP-Systems and this gave me the chance to gain insight into his abilities and traits.

He is an ambitious student and has improved his skills steadily. I can attest that his performance has been consistently good and he has always behaved responsibly. Also, he is systematic and organized at work and has shown a predilection for applied economics.

As for his personal qualities, Mr. [NAME] is a well-disciplined, industrious student with a pleasant personality. He has always been a very open and respectful student who demonstrates a great capacity for integration into university life.

For all these reasons, I highly recommend this candidate to you. Furthermore, I believe that your program will provide him with valuable experience, helping him to improve his English level, and deepen his understanding of foreign cultures and values.

Should you need further information, please feel free to contact me at the address above.

Yours faithfully,

My only other comment is that "systematic and organized" seems to be part of "well-disciplined" so it seems redundant in the paragraph above, but there's no grammatical problem.