Based on the description you provided it can be of three types:
Small, white, circular pill
Name: Methylin 10 mg
Manufacturer: Mallinckrodt
Info: Methylphenidate is a central nervous system stimulant. It affects chemicals in the brain and nerves that contribute to hyperactivity and impulse control. Methylphenidate is used to treat attention deficit disorder (ADD), attention deficit hyperactivity disorder (ADHD), and narcolepsy.
Small, white, square pill with rounded edges
Name: Dextroamphetamine-amphetamine 10 mg
Manufacturer: Mallinckrodt
Info: They are used to treat attention-deficit hyperactivity disorder (ADHD). Amphetamines increase attention and decrease restlessness in patients who are overactive, unable to concentrate for very long or are easily distracted, and have unstable emotions.
Small, white, diamond pill with rounded edges
Name: Dextroamphetamine sulfate 10 mg
Manufacturer: Mallinckrodt
Info: Dextroamphetamine is a central nervous system stimulant. It is used for treating attention deficit disorder with hyperactivity in children. It is also used to treat a type of sleep disorder (narcolepsy). It may also be used for other conditions as determined by your doctor.