 The unit block principle was popularized by educator Caroline Pratt in the early 1900s.Pratt based her blocks on a similar but larger-scale block system designed by educator Patty Hill, a follower of Friedrich Fröbel, the originator of kindergarten education.Fröbel's series of 20 age-calibrated educational "gifts" had included a set of eight blocks, sized ½ by 1 by 2 inches, or a 1