If you are doing this for the money you may want to find a different job. Also kids are extra unruly for substitutes so it can be a challenge to keep them in line. The biggest need is for the elementary age which I have found to require more effort and you have less chance to teach your expertise but I like keeping busy. Sometimes positions are just babysitting, which is fine if you are there for the money but I generally avoid those positions as I am not there to be bored.