Introduction: Certain behaviors associated with high intellectual ability, such as inattention and early response, are often confused with attention deficit and hyperactivity disorder (ADHD), making correct diagnosis more difficult. The objective of the present study was to analyze the performance of students with high intellectual ability and students with ADHD in sustained attention and impulsivity. Method: Participants included a total of 25 children with high intellectual ability and mean age of 6.15 years, and 25 children with ADHD and mean age of 6.96 years. "Conner's Continuous Performance Test II" for Windows (CPT II) was administered to all participants. An ex post facto methodology was followed. The results were analyzed statistically, using SPSS, through a t test for independent samples. Results: Significant differences were found in Omissions, Hit Reaction Time, Reaction Time Standard Error and Hit Reaction Time at Change of Inter-Stimulus Interval Discussion and conclusions: (1) Children with high intellectual ability have significantly better consistency in response speed, better consistency in reaction times at different interstimulus intervals, and make greater errors of commission compared to students with ADHD. (2) Children with high intellectual ability perform significantly faster when answering correctly during the test. Performance tests such as the CPT-II for the measurement of attention and impulsivity represent an alternative assessment, with differential diagnosis between these populations. This process must be carried out by qualified personnel who have experience with both populations.