Yesterday I was doing a presentation about prefixes to two students, one age 6 and one age 7. I was using alphabet tiles and putting down root words in blue. The first word I put down was "play." We talked about the different meanings of the word, not too difficult to define. Then we would make the root word again in blue, and I would add "a little bit" to the beginning to change its meaning ("re-", "dis-") and we would talk about the new meaning now that we'd added the "little bit," which we later termed "prefix."
We did several words this way. For the children to define a term without using the term in their definition was challenging, but they put forth a good effort and did a great job. I was, though, blown away by the seven year olds definition of the verb "tie."
First he said, "you know, to tie a knot." When I challenged him to define it without using the word "tie" he got quiet a minute to think, and then...
"well, to secure a bow."
I couldn't have said it better myself...really.