Which kind of supplements is the best for boosting memory and focus for students?

Many good options. I advise the herb rhodiola first. B vitamins may help (esp. B12 if you're deficient). Phosphatidylserine, acetyl-l-carnitine, bacopa, vinpocetine, ashwagandha, gingko, dmae, hydergine & piracetam are all proven to help. There are entire books on this subject. A good article is at http://www.Smart-publications.Com/articles/be-smarter-think-faster-and-protect-your-brain-with-12-smart-nutrients.