Cognitive abilities and executive functions in children and adolescents are important indicators of quality of life as well as academic and social achievements. Cognitive and executive functioning are often impaired in patients with epilepsy and can be exacerbated by seizures and antiseizure drugs. The aim of our observational retrospective study was to assess executive functioning in patients with pediatric epilepsy, currently taking a single antiseizure medication. Records of 172 children and adolescents aged between 6 and 18 years (mean age = 12 ± 3.4 years) with newly diagnosed epilepsy who had not yet commenced an antiepileptic treatment were included in the study. Longitudinal changes in executive functioning were assessed using the EpiTrack Junior test at baseline, before the introduction of antiepileptic monotherapy, and at 3-month, 6-month, and 9-month follow-up visits. All patients commenced a single antiepileptic treatment (levetiracetam n = 54; valproic acid n = 52; ethosuximide n = 20; oxcarbazepine n = 22; carbamazepine n = 24). Age, sex, seizure types, and seizure baseline frequency were also recorded. Relative to baseline, Epitrack Junior mean scores deteriorated at the 9-month follow-up visit for patients taking valproic acid, ethosuximide, and carbamazepine, but this was only statistically significant for patients taking carbamazepine. In contrast, mean scores improved for subjects taking levetiracetam and oxcarbazepine at the 9-month follow-up visit relative to baseline, but this was only statistically significant for patients taking levetiracetam. Levetiracetam was the only antiseizure medication that led to slight improvements in executive functioning; whereas carbamazepine led to deteriorations in cognitive functioning. Further research using double-blinded, placebo-controlled trials are needed to confirm these results.