This file is an idependent math center in which students practice two or three digit addition. The center consists of a student instruction sheet and aliens with numbers on their bellies. Students pull two aliens, write the addition problem, and solve. The file contains four seperate sheets of aliens: one set for two-digit with regrouping, one set for two-digit without regrouping, one set for three-digit with regrouping, and one set for three-digit without regrouping.