Requiring students to create weed collections is a common technique for teaching weed identification. Data compiled over 18 years from students' weed collections in a college-level course included over 350 species of plants. Almost half of the specimens belonged to the Asteraceae or Poaceae. The 30 most frequently collected species accounted for almost two-thirds of the specimens but "Chenopodium album" L., the most frequently collected species, accounted for only 4.8% of the total. Overall, 73.1% of specimens were correctly identified to species. Five species ("Abutilon theophrasti" Medik., "Vicia cracca" L., "Portulaca oleracea" L., "Plantago major" L., and "Asclepias syriaca" L.) were correctly identified at least 97% of the time. Misidentification was highest with "Scorzoneroides autumnalis" (L.) Moench [synonym (syn.) "Leontodon autumnalis" L.], "Malva neglecta" Wallroth, "Erysiumum cheiranthoides" L., "Echinochloa crus-galli" (L.) Beauv., and "Erigeron canadensis" L. (syn. "Conyza canadensis") and within the genera "Sonchus" L., "Setaria" P. Beauv., and "Digitaria" Haller. Misidentification was the lowest in the Equisetaceae, Apocynaceae, Oxalidaceae, and Plantaginaceae and highest in the Lamiaceae, Poaceae, Brassicaceae, and Asteraceae. Variability in individual species' morphology may have contributed to misidentification.