Does stopping ritalin on weekends help avoiding having tolerance on methylphenidate and the need of larger doses ?

Not a bad approach: In my experience, Ritalin (methylphenidate) is notorious for progressive tolerance (tachyphylaxis), and often have seen need for dosage adjustment within a period of a few months. However, not taking the drug daily, and having a mini-vacation seems to prolong efficacy at current dose in many patients. Your weekend plan may work very well and worth a try, if you do not have withdrawal effect. Discuss with doc.

Depends: This is the way i prescribe it. It is primarily used as an aid to the "work" of the student who needs to focus, and during weekends when s/he is off "work" there is value in being in their normal state, if not too problematic. I don't see much tolerance in kids, and limiting the med during their growing years limits the impact on that process.