There are several interesting things to discuss when teaching this root word, jacio, jactum. Remember that in Latin, "j" is pronounced as though it were a "y". Actually, the ancient Romans didn't juse "j" at all. They spelled this word, "iacio, iactum". When you remember to pronounce "i" with a long "ee" sound, and say this word out loud, you can see where the "y" sound came from. Julius Caesar's name was spelled "Iulius Caesar". Medieval scribes who made those beautifully illuminated handwritten manuscripts started adding a decorative "tail" to the letter "i" when it came at the beginning of a word. Also, a word (such as the Latin word, huius) which had three vowels in a row was confusing to read. (Try writing it in cursive ) They dotted the "i", of course, but drawing it down into a "tail" made it much easier to read.
You notice that all the derivatives above have a -ject spelling. The Romans tended to shift the vowel to a short sound when they added a prefix to the word. So iacio became conicio, coniectum. The medieval scribes wrote it conjectum and we have our word conjecture which means literally, "throw together". When we are trying to figure out something, we throw together the clues we have nad come up with a conjecture, a supposition, a guess. The root idea "throw" is so easy for children to understand, they can readily understand the derivatives we have from "Jacio, Jactum" when we explain how these "throw" words are used metaphorically for various mental actions such as "rejecting" and objecting".