Common Core Standards
Grade 2
Language L.2.4.B
Determine the meaning of the new word formed when a known prefix is added to a known word (e.g., happy/unhappy, tell/retell).
Second gaders should know that adding a prefix to a word can change the meaning of that word. Using knowledge they've already got and building on it will be key in the coming years, so this a necessary substandard to nail.