Here are some of the instruments that are typically used by myself and my colleagues for ADHD assessments:
Conners Rating Scale - Revised (revised version of this test has much better norms that the old version; this test is probably the most widely used across professions - physicians, psychologists, counselors, social workers and teachers);
Behavior Assessment System for Children or the Child Behavior Checklist (both instruments provide a broad-based assessment of symptoms besides those of ADHD which helps the clinician rule out competing disorders; the BASC is a better instrument, in my opinion, because it contains separate scales for inattention and hyperactivity/impulsivity where the CBC lumps these two areas together in one scale);
Brown Attention Deficit Disorder Scales or the Conners-Wells Self-Report Rating Scale - both are self-report rating scales which are used with individuals from 12 - 18. It's nice to have instruments which can be used to report s