What's the effect of stimulants on kids with adhd?

Typically quite good. Stimulants are by far the most thoroughly studied medications used to treat a child psychiatric disorder. 65-85% of the time, they markedly decrease key symptoms of inattention, poor focus, impulsivity, & hyperactivity. They work quickly but also wear off daily. Side effects are well known, dose-related, & for most kids tolerable. Sadly, they do not "cure" adhd, nor are they the whole answer.
Stimulants. They improve attention span, lessen distractability, and calm them down when impulsivity is reduced. Some experience decrease appetite & insomnia.
Improve symptoms. If your child actually has ADHD, stimulant medication should improve their ability to focus, attend and resist distractions in school. Medication may help with impulsivity so that socializing with other children may improve. Improvement in impulsivity should also provide a positive effect on safety in impulsive children.
Beneficial in ~ 90% They are meds that "stimulate" parts of the brain that inhibit behavior. The ability to stop & think about consequences of one's actions allows a child to learn more adaptive behaviors & social skills. Attention & memory interface, so learning is easier. Being able to hold onto information till you have to act on it helps you in math & direction-following, so you garner :)'s from adults.
Effects of Stimulant. The effects are "paradoxical, " that is, they seem to slow kids down rather than speed them up. While this is largely theoretical, there are changes in brain chemistry as a result of the medications. Side effects can be temporary suspension of physical growth and loss of appetite - both of which return rapidly when the medicine is discontinued.