What is onset of action, peak, and duration of effect for ritalin (methylphenidate)?

Varies: It varies with individual, food, other drugs, other conditions. Textbook says 1 hr, 2 hr, 3-4 hr: but this hardly definitive.

Varies with delivery: There are many delivery systems that use Ritalin (methylphenidate) (methylphenadate) as its primary drug. The difference in the delivery system effects the peak and duration. The simple basic drug peaks around 2 hours and is gone by 4. Concerta, which uses a specialized delivery system is thought to achieve a good level by 2 hours and sustain it for another 4, before tapering off, gone by 8-10.

Depends on form: Ritalin (methylphenidate) in tablet form usually takes 30 to 45 minutes to begin working. It will peak in approximately 2 hours and the effect will last approximately 4 hours. Longer duration forms of methylphenidate (Ritalin LA) effect lasts approximately 8 hours and Concerta effect lasts from 10 to 12 hours.